I overdid it with this one, I'm sure of it.  But probably better I get out all of my ideas first and then figure out which ones work and which ones don't I suppose.  All of the perfected golem abilities are word-for-word similar to as they appear in their respective golems' monster stat blocks in the Monster Manual.  Inspired by this comment and related forum thread posts.

The Golem Crafter

3rd Level: Tools of the Trade

• You gain proficiency with Woodcarver’s tools and a free set of Woodcarver’s tools.
• Artisan tool proficiency & free artisan tools based on type of personal golem crafted:
  • Clay golem: potter’s tools
  • Iron golem: smith’s tools
  • Stone golem: mason’s tools
  • Flesh golem: leatherworker’s tools
• You gain the ability to use rods, staffs, and wands as spellcasting focuses for your artificer spells.
• You also gain a nonmagical, wooden staff or wand for free, which you’ve carved in your spare time.
• If you craft a magic item in the rod, staff, or wand category, it takes you a quarter of the normal time, and it costs you half as much of the usual gold.

3rd Level: Golem Crafter’s Spells

• Choose your type of golem — clay, iron, or stone — and consult the associated list of spells.

3rd Level: Bonus Cantrips

• At 3rd level, you learn a cantrip based on which type of personal golem you crafted. This cantrip counts as an artificer cantrip for you, but it doesn’t count against your number of cantrips known.
  • Clay golem: acid splash
  • Iron golem: fire bolt
  • Stone golem: ray of frost
  • Flesh golem: shocking grasp

3rd Level: Personal Golem

• Your time spent studying runes & elemental magic during your adventures has caught the attention of a spirit from the Elemental Plane of Earth. You bond with this spirit, inevitably constructing a golem body in your spare time to give the spirit a physical form to house itself in.  This bond is then forever sealed by inscribing your personal rune onto the body of the personal golem, fully activating it for the first time.
• Battle Smith’s Iron Defender as base, stats modified to reflect stats of a clay/iron/stone golem
  • In combat, the personal golem shares your initiative count, but it takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take one of the actions in its stat block or the Dash, Disengage, or Help action.
  • If the mending spell is cast on the personal golem, it regains 2d6 hit points.
  • If the related cantrip spell is cast on the personal golem, the spell automatically deals damage to the personal golem. The personal golem takes no damage from the spell and instead regains a number of hit points equal to the damage dealt.
    • The personal golem suffers no other adverse effects from the cantrip cast on it, if any (i.e. ray of frost doesn’t reduce its speed by 10 ft after the spell hits, etc.)
  • If the personal golem has died within the last hour, you can use your related artisan’s tools as an action to revive it, provided you are within 5 ft. of it and you expend a spell slot of 1st level or higher; it returns to life after one minute with all of its hit points restored.

6th Level: Crafter’s Crutch

• By 6th level, you have carved many runes onto a number of staffs, wands, and even the occasional rod and magic weapon, although you don’t know how many these items number or where they all are. Whenever you finish a long rest and your woodcarver’s tools or related artisan’s tools are with you, you may activate up to two of these runes on any rod, staff, wand, or weapon in your possession at a time.
  • An item cannot have more than one rune activated at a time.
  • Any creature that can cast a spell can use an item with at least one rune activated on it as a spellcasting focus.
  • Each rune’s effects can only be used while a creature is holding an item the rune is activated on.
  • Simply having a rune carved onto an item does not make it magical; an item becomes magical after activating at least one rune on it, if it wasn’t magical already.
  • All activated runes become deactivated at the end of a long rest.
  • At 14th level in this class, you may activate up to three runes on any rod, staff, wand, or weapon in your possession at a time. In addition, one item may have up to two runes activated on it, but you cannot have more than one rune of the same type activated on an item.
• Life Rune:
  • This rune can only be activated on a wooden staff or a wooden wand.
  • Any creature holding an item this rune is activated on that can cast at least one spell can cast cure wounds at 2nd level without expending a spell slot using your Intelligence modifier and using the item as the focus once for every Life Rune you have activated.
  • You can cast lesser restoration without expending a spell slot a number of times per day equal to your Intelligence modifier (minimum of once) while you’re holding an item this rune is activated on and using the item as the focus.
  • Any spell you cast that restores hit points gains a bonus equal to your Intelligence modifier (minimum of +1) while you’re holding an item this rune is activated on and using the item as the focus.  You get this bonus only once even if you have more than one Life Rune activated.
  • You can cast spare the dying even if you don’t know the cantrip while you’re holding an item this rune is activated on and using the item as the focus.
  • At 14th level in this class:
    • You can cast death ward using your artificer spell slots while you’re holding an item this rune is activated on and using the item as the focus.
    • You can cast greater restoration once without expending a spell slot and without providing the material component while you’re holding an item this rune is activated on and using the item as the focus even if you have more than one Life Rune activated.
    • You can cast raise dead once without needing materials or spending a spell slot while holding an item with this rune activated on it and using the item as the focus. Because of the amount of magic involved, once you use this ability you cannot use it again from any Life or Death Rune you activate for ten days.  Using this ability immediately deactivates all of your activated Life and Death Runes after the spell resolves.
  • Mage Rune:
    • This rune can only be activated on a rod, a staff, a wand, or a one-handed melee weapon that doesn’t have the reach property.
    • Any creature holding an item this rune is activated on that can cast at least one spell can use the item as a spellcasting focus.
    • Any creature holding an item this rune is activated on that can cast at least one spell can cast your related cantrip using your Intelligence modifier & spell save DC and using the item as the focus.
    • Any damage roll you make for your related cantrip gains a bonus equal to your Intelligence modifier (minimum of +1) while you’re holding an item this rune is activated on and using the item as the focus. This bonus does not stack with the bonus from a Death Storm Rune.  You only get this bonus once even if you have more than one Mage Rune activated.
      • At 14th level in this class, this bonus also applies to any spell or magical effect you cast that deals related cantrip damage while using the item this rune is activated on as the focus.
    • At 14th level in this class:
      • You can cast one artificer cantrip of your choice—even one you don’t know—that has a casting time of 1 action while you’re holding an item this rune is activated on and using the item as the focus. You choose the artificer cantrip when you activate this rune on an item.  Any damage roll you make for this cantrip gains a bonus equal to your Intelligence modifier (minimum of +1). You only get this bonus once even if you have more than one Mage Rune activated.
      • As an action, you can point at a location that you can see within 150 ft, and a glowing, 1-foot-diameter ball of swirling emerald, ruby, and sapphire energy streaks there and explodes in a 20-foot-radius sphere. Each creature in that area must make a Dexterity saving throw. On a failed save, a creature takes 10d4 related cantrip damage and another 5d4 related cantrip damage at the end of its next turn. On a successful save, a creature takes half the initial damage and no damage at the end of its next turn. You can do this once for every Mage Rune you have activated.
    • Might Rune:
      • This rune can only be activated on a rod, a staff, a wand, or a one-handed melee weapon that doesn’t have the reach property.
      • Any creature holding an item with this rune activated on it gains the following benefits:
      • An item with this rune is activated on it counts as a simple melee weapon. The item’s weapon damage die is 1d8.  In addition, the item counts as a magic weapon and gains a +1 bonus to attack and damage rolls, unless it is a magic weapon that already has a bonus to those rolls.  This bonus increases to +2 at level 14.  This bonus does not stack with the bonus gained from a Storm Rune or from having more than one Might Rune activated.
        • Wand: This item can be wielded as a club.
        • Rod: This item can be wielded as a mace.
        • Staff: This item can be wielded as a quarterstaff.
      • Any creature holding an item with this rune activated on it may use their Intelligence modifier, instead of Strength or Dexterity, for attack & damage rolls made with this item.
      • You may attack twice when you take the Attack action on your turn while you’re holding an item with this rune activated on it.
      • When you hit a creature with a melee weapon attack while holding an item with this rune activated on it, you can expend one spell slot to deal related cantrip damage to the target, in addition to the weapon’s damage. The extra damage is 2d8 for a 1st-level spell slot, plus 1d8 for each spell level higher than 1st, to a maximum of 5d8.
      • At 14th level in this class, when you use your action to cast an artificer spell, you can make one weapon attack as a bonus action while you’re holding an item with this rune activated on it using the item to make the attack.
    • Storm Rune:
      • This rune can only be activated on a rod, a staff, or a one-handed melee weapon that doesn’t have the reach property.
      • Any creature holding an item with this rune activated on it gains the following benefits:
      • An item with this rune activated on it counts as a simple melee weapon that deals 1d8 lightning damage and has the finesse, light, and thrown properties (range 30/120); it returns to the wielder’s hand immediately after it is used to make a ranged attack. In addition, the item counts as a magic weapon and gains a +1 bonus to attack and damage rolls, unless it is a magic weapon that already has a bonus to those rolls.  This bonus increases to +2 at level 14.  This bonus does not stack with the bonus gained from a Might Rune or from having more than one Storm Rune activated.
        • Rod: This item can be wielded as a mace.
        • Staff: This item can be wielded as a quarterstaff.
      • Any creature holding an item with this rune activated on it can use it as a spellcasting focus when casting a spell that deals lightning or thunder damage.
      • You may attack twice when you take the Attack action on your turn while you’re holding an item with this rune activated on it.
      • Any thunder damage roll you make gains a bonus equal to your Intelligence modifier (minimum of +1) while you’re holding an item this rune is activated on and using the item as the focus. This bonus does not stack with the bonus gained from a Mage Rune or from having more than one Storm Rune activated.
      • Whenever you make an opportunity attack using an item this rune is activated on, on a hit the target suffers an extra 1d8 thunder damage, and it becomes sheathed in booming energy until the start of your next turn. If the target willingly moves before then, it immediately takes 2d8 thunder damage. Both damage rolls increase by 1d8 at 11th level and 17th level in this class.
      • Whenever you make a ranged weapon attack using an item this rune is activated on, you can transform it into a bolt of lightning. Make the attack roll as normal. The target takes 4d8 lightning damage on a hit, or half as much damage on a miss, instead of the weapon’s normal damage. Whether you hit or miss, each creature within 10 feet of the target must make a Dexterity saving throw. Each of these creatures takes 2d8 lightning damage on a failed save, or half as much damage on a successful one.  You can do this once for every Storm Rune you have activated.
      • At 14th level in this class:
        • You have thunder resistance while you’re holding an item this rune is activated on.
        • You can cast call lightning and lightning bolt using your artificer spell slots while you’re holding an item this rune is activated on and using the item as the focus.
        • You gain a flying speed of 60 ft while you’re holding an item with this rune activated on it. If you are still flying at end of your turn and you’re not holding an item with this rune activated on it, you fall, unless you can somehow prevent it.
      • Death Rune:
        • This rune can only be activated on a wooden staff or a wooden wand.
        • Any creature holding an item this rune is activated on that can cast at least one spell can use the item as a spellcasting focus.
        • Any creature holding an item this rune is activated on that can cast at least one spell can cast chill touch using your Intelligence modifier & spell save DC and using the item as the focus.
          • If you cast chill touch on the personal golem and its golem type is flesh golem, the spell automatically hits. The personal golem takes no damage from the spell and instead regains a number of hit points equal to the damage dealt.  You must be holding an item with this rune activated on it and using it as the focus.
            • The personal golem can still regain hit points even if it’s hit by chill touch.
          • Any damage roll you make for chill touch gains a bonus equal to your Intelligence modifier (minimum of +1) while you’re holding an item this rune is activated on and using the item as the focus. This bonus does not stack with the bonus gained from a Mage Rune.
        • You can cast animate dead without expending a spell slot once for every Death Rune you have activated while you’re holding an item this rune is activated on and using the item as the focus.
          • Animate dead can target the corpse of the personal golem. Casting animate dead on your dead personal golem returns it to life with all of its hit points restored.
        • At 14th level in this class:
          • You have necrotic resistance while you’re holding an item this rune is activated on.
          • Any necrotic damage roll you make gains a bonus equal to your Intelligence modifier (minimum of +1) while you’re holding an item this rune is activated on and using the item as the focus. This bonus does not stack with the bonus gained from a Mage Rune.
          • Whenever you cast a spell that deals necrotic damage while you’re holding an item this rune is activated on and using the item as the focus, that spell can affect undead creatures even if the text of the spell says otherwise.
          • You can cast blight using your artificer spell slots while you’re holding an item this rune is activated on and using the item as the focus.
          • You can cast raise dead once without needing materials or spending a spell slot while holding an item with this rune activated on it and using the item as the focus. Because of the amount of magic involved, once you use this ability you cannot use it again from any Life or Death Rune you activate for ten days.  Using this ability immediately deactivates all of your activated Life and Death Runes after the spell resolves.

6th Level: Improved Golem

• During your time adventuring with the personal golem, you’ve researched or discovered new runes to improve its performance in the following ways:
  • The personal golem’s attacks are considered magical for the purposes of bypassing resistances and immunities.
  • The personal golem gains resistance to bludgeoning, piercing, and slashing damage from nonmagical attacks not made with adamantine weapons.
  • The personal golem gains related cantrip damage immunity & fortification; it takes no damage, instead it gains temporary hit points equal to half the damage dealt rounded up.
    • While the personal golem has these temporary hit points, it gains a +2 bonus to its AC, melee attack rolls, and damage rolls.
  • If the personal golem has died within the last hour, you can expend the energy in one of your activated runes as an action to revive it, provided you are within 5 feet of it. The personal golem returns to life after 1 minute with all its hit points restored. Using this ability deactivates one of your activated runes of your choosing.

14th Level: Perfected Golem, Perfected Self

• You’ve expanded your knowledge of elemental magic in many of its forms. You can now attune to any magic item that a druid or a wizard can attune to.
• You gain related cantrip resistance. Justifications for related resistances:
  • Acid: you’ve been experimenting with different acids to improve the quality of the clay used in the personal golem.
  • Fire: you’ve spent countless hours at a forge working to improve the quality of the iron used in the personal golem.
  • Cold: you’ve mined on top of the coldest peaks & inside the deepest caverns for ore to improve the quality of the stone used in the personal golem.
  • Lightning: you’ve worked with A LOT of electricity animating the flesh used in the personal golem.
• You’ve learned even more runes to perfect the personal golem in the following ways:
  • The personal golem’s darkvision range increases to 120 ft.
  • The personal golem gains Multiattack (can make two slam attacks).
    • You can use your bonus action to order personal golem to make a multiattack on its next turn.
  • The personal golem gains magic resistance (Advantage on saving throws vs. spells/other magical effects).
    • When the personal golem is affected by a spell or magical effect that deals related cantrip damage to it, the personal golem may automatically fail its saving throw against the spell or magical effect.
  • The connection between you and your rune on the personal golem has grown stronger over time, allowing you to channel more of your magic through the personal golem now. When you cast a spell with a range of touch, the personal golem can deliver the spell as if it had cast the spell. The personal golem must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it. If the spell requires an attack roll, you use your attack modifier for the roll.
  • The personal golem gains a perfected golem ability based on its golem type:
    • Clay golem: haste (recharge 6): until the end of its next turn, the personal golem magically gains a +2 bonus to its AC, has advantage on Dexterity saving throws, and uses its slam attack as a bonus action on its turn.
    • Iron golem: poison breath (recharge 6): the personal golem exhales poisonous gas in a 15-foot cone. Each creature in that area must make a Constitution saving throw against the golem crafter’s spell save DC, taking 45 (10d8) poison damage on a failed save, or half as much damage on a successful one.
    • Stone golem: slow (recharge 6): the personal golem targets one or more creatures it can see within 10 feet of it. Each target must make a Wisdom saving throw against the golem crafter’s spell save DC.  On a failed save, a target can’t use reactions, its speed is halved, and it can’t make more than one attack on its turn.  In addition, the target can take either an action or a bonus action on its turn, not both.  These effects last for 1 minute.  A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
    • Flesh golem: Berserk: whenever the personal golem starts its turn with less than half of its maximum hit points, roll a d6. On a 6, the personal golem goes berserk.  On each of its turns while berserk, the personal golem attacks the nearest creature it can see.  If no creature is near enough to move to and attack, the personal golem attacks an object, with preference to an object smaller than itself.  Once the personal golem goes berserk, it continues to do so until it is destroyed or regains all of its hit points.  The golem crafter, if within 60 feet of the berserk personal golem, can use a bonus action to try to calm it down by speaking firmly and persuasively.  The personal golem must be able to hear the golem crafter, who must make a DC 15 Charisma (Persuasion) check.  If the check succeeds, the personal golem ceases being berserk.  If it takes damage while still at less than half its maximum hit points, the personal golem might go berserk again.

PERSONAL GOLEM

Medium construct, neutral

Armor class 15 (natural armor)

Hit Points equal to five times your level in this class + your Intelligence modifier + the personal golem’s Constitution modifier

Speed 30 ft.

Strength 14 (+2)

Dexterity 10 (+0)

Constitution 14 (+2)

Intelligence 6 (-2)

Wisdom 10 (+0)

Charisma 6 (-2)

Skills Perception +4

Damage Immunities poison, psychic

Condition Immunities charmed, exhaustion, frightened, paralyzed, petrified, poisoned

Senses darkvision 60 ft., passive Perception 10

Languages understands the languages you speak but cannot speak

Immutable Form: The personal golem is immune to any spell effect that would alter its form.

Might of the Master.  The following numbers increase by 1 when your proficiency bonus increases by 1: the personal golem’s armor class, skill bonuses, and the bonuses to hit & damage with its slam attack.

Vigilant.  The personal golem cannot be surprised.

Actions (Requires Your Bonus Action)

Slam.  Melee Weapon Attack: +4 to hit, reach 5 ft., one target you can see.  Hit: 1d8 + 2 bludgeoning damage.

Edited to include preliminary revisions.

Oh wow. That IS OP...

Seems like you merged the flesh golem subclass you created with the Rune Scribe prestige class from a few years ago. Both can be their own class, so together they are just too much for the player to keep track of...

I like how there are different types of golems, feels like the Giant Soul subclass of the Sorcerer in that regard. Might want to have the base subclass spells also change according to the golem chosen (example in both Giant Soul Sorcerer and the Circle of the Land Druid)

Also like how the tool depends on the golem created as well, though I'd recommend the magic item to be just one type as three might be too much... How about just staffs?

Do note that artificers have pretty much free reign with their spellcasting focus (official examples including a tiny clockwork spider) so they technically can use anything as a spellcasting focus "as rules written" and "as rules meant" currently. Specifying they can use wands and such seems unnecessary.

As for the two-class problem, the Artillerist also suffers from this so it may be a non-issue.

Quote from NeoPhantom >>

Oh wow. That IS OP...

Seems like you merged the flesh golem subclass you created with the Rune Scribe prestige class from a few years ago. Both can be their own class, so together they are just too much for the player to keep track of...

I like how there are different types of golems, feels like the Giant Soul subclass of the Sorcerer in that regard. Might want to have the base subclass spells also change according to the golem chosen (example in both Giant Soul Sorcerer and the Circle of the Land Druid)

Also like how the tool depends on the golem created as well, though I'd recommend the magic item to be just one type as three might be too much... How about just staffs?

Do note that artificers have pretty much free reign with their spellcasting focus (official examples including a tiny clockwork spider) so they technically can use anything as a spellcasting focus "as rules written" and "as rules meant" currently. Specifying they can use wands and such seems unnecessary.

As for the two-class problem, the Artillerist also suffers from this so it may be a non-issue.

 Yeah, all the stuff pertaining to flesh golems and the Storm & Death Runes were added in last minute.  My original design intent for this subclass was to focus on the other three types of golems since I already figured out enough to do with a flesh golem in my Mad Scientist subclass.  But then I figured, if I could find a way to fold in the flesh golem, I might as well do it anyway and just remove it later if the subclass became too clunky.  Which clearly it is lol

I threw in all the wording about focuses and stuff because it's literally the same wording used in the Artillerist's proficiencies.  But I'm narrowing down their crafting expertise to just staffs now since staffs are the only consistent item any of the runes I designed could be activated on.

I'll definitely need to check out that Giant Soul Sorcerer subclass later.  And I feel dumb for not even remembering how Circle of Land druids have eight separate spell lists for each different terrain.  Separate spell lists based on what type of golem you craft makes more sense than whatever tf it is that I tried to do XD

I may still leave in the Storm Rune stuff.  I enjoyed how between this subclass and the Mad Scientist I almost successfully covered the five major elemental resistances in the game.  Also, I absolutely had a Thor-like play-style in mind when I was designing the Storm Rune so I think others will appreciate that as well.  But if that also gets too cumbersome, I'm sure I can eventually let it go as well.

OP updated to reflect current preliminary revisions:

• Scrapping all the flesh golem and Death Rune stuff. 
• Making the crafting expertise specifically staffs only.
• Cleaned up the item-interaction language to make it look less clunky I hope.
• Made separate spell lists for each type of golem crafted.

Looking forward to any more feedback for this.

Edited to include the staffs-only revised crafting expertise.