Hello All, 

Just wanted to get some feedback on this new magic armour system I created and even perhaps get some ideas thrown around to add!

The Concept: New armours can be discovered at first with no magic effects found on them. The players notice that there are faded markings and can take them to an NPC I created and have deciphered and restore the marking(s) thus restoring the magic properties (at a cost of GP/ ingredient items, etc.). The effects are determined by a 1d20 roll where each value is a different effect. Each armour piece can have either 1, 2, or 3 total effects. There are 3 tiers of effects with each tier getting gradually more powerful but at cost. The 1st tier consists of simple, lower benefit effects, the 2nd tier consists of various damage resistances and, the 3rd tier consists of very powerful effects but comes with a greater negative effect. 

Note: The examples I provided are just a few from the full list of 20+ possible effects the players could get from each tier.

1st Tier: Faded Runes - examples effects include: Faded Rune of the Silver Tongue (+1 to CHA)    Faded rune of Strength (+1 to STR)    Faded rune of the Third Eye (+1 to Investigation, perception, and insight).

2nd Tier: Warding Runes - examples:  Flame Warding (Take half as much fire damage from any source).   Poison Warding (Take half as much poison damage from any source).   Magic Warding (Take 1/4 as much magic damage from any source).   Physical warding (Take 1/4 as much physical damage from any source).

3rd Tier: Accursed Runes - Goetic Rune (When near death, add 25 points of damage to your overall amount of damage dealt this turn).  Note: The DM decides what "Near Death" qualifies as. I was thinking of anywhere between 1-5 points of health left. 

Cursed pact of the Warlock (Take 1/2 as much magic damage from any source but twice as much physical damage from any source).  Note: Cursed Earth Pact does the inverse of this effect.

Mark of the Black Flame (All flames or fire based attacks the player has, the flames turn to an abyssal black and deal twice as much damage to holy creatures and no damage to anything undead, demonic, or fiendish. Everything else takes normal damage). 

Rune of Greed  (You may cast a spell that you couldn't otherwise have cast but at the cost of half your current health rounded up. You may also double the amount of gold or platinum found but at the same cost. This runes power can only be used once per day).

Suppression Scar (1 charge, requires long rest to recharge. Everything in a 30-foot radius of the activating player losses all ability to use spells, magic, magic abilities, magic items, and other runes for 1 in-game minute).

Let me know if you have any suggestions, questions, or additions to the system. I have not playtested the concept yet btw. Just wanted to get it refined as much as possible before implementing.

Thanks in advance! 

Is this kind of like the example sentient item in the DMG, the Moonblade? In the DMG, a Moonblade is passed down through the generations in a house of elves. Each time it changes hands, a new rune appears on the blade, giving the weapon a new functionality or ability. Is this your basis? Also, another few ideas:

Edit: New Rune Ideas + Old ones in new format

1st Tier:

Faded Rune of the Nimble Finger (+1 to DEX)

Faded Rune of the Sturdy Heart (+1 to CON)

Faded Rune of Knowledge (+1 to all checks with intelligence modifiers) 

Faded Rune of Sight in the Gloom (You gain Darkvision to 30 feet, unless you already have it, in which case, your range extends to 60 feet).

Faded Rune of the Wise Tome (You can spend an hour doing a ritual that transforms an empty book into an arcane book of wisdom. When the book is on your person, you get a +2 to your Wisdom score. When you are incapacitated, this bonus does not work. If the book is destroyed, you can choose a new book, and do another ritual to recreate your book)

2nd Tier:

Damage Warding (Recharges after a long rest. You can spend an action to give yourself 100 temporary hit points. These hit points last until the end of your next turn, in which you lose hitpoints equal to 1.5 times the remaining hit points. If this makes you drop to 0 hitpoints, you are instantly stable.)

Mental Warding (Once per turn, take 1/4 psychic damage from one source)

Acidic Warding (You have resistance to Acid damage)

Cursed Warding of The Corporeal (You have resistance to two of the damage types you choose, and you gain vulnerability to the other. The damage types are as following: Bludgeoning, Piercing, and Slashing)

Note: For all of these that you take half damage, you can rewrite that as "resistance." Resistance in D&D 5e is taking half damage, while vulnerability takes  2 times damage (you always round up).

3rd Tier:

Rune of the Invisible Devourer (As an action (only in combat), you can turn invisible. For every round in combat that you stay invisible, you take 1d4 psychic damage. Each round that increases by a d6 to a maximum of 20d6. This total resets after a long rest is taken)

Mark of Allure  ((2 charges, requires a long rest to regain 1 charge) Every piece of metal within a 30 foot radius is attracted to you. Attacks with metal weaponry have advantage on attack roles against you, and for every creature pulled, in add this damage to all of the creatures pulled in. 1d4 for Tiny, 2d4 for Small, 2d6 for Medium, 3d8 for Large, 4d10 for Huge, and 5d12 for Gargantuan (All of this is force damage). Note: This works well with the Cursed Eath Pact. Edit: You can expend another charge to repel the creatures away. each creature attacked to you takes 2d10 + 5 force damage and is pushed 30 feet from you in a random direction. You take 1d6 + 2 force damage for every creature "attached" to you)

Cursed Pact of Sight (You have Truesight for a range of 60 feet, but you have disadvantage on a roll to see things (Perception, Investigation, Insight, etc). A Critical Success counts as a critical failure. All spell attacks have disadvantage unless you are within half of the range of the maximum distance (Edit: If under 5 feet, attacks work as normal. If an odd number of feet, round up))

Note: For the Suppression Scar, you can give it one charge and have it be the ability to cast Antimagic field, just to make it simpler.

I actually had no idea about the moonblade. I really like that idea of the item changing properties for each owner. Made me think of the Moonlight Greatsword from the Dark Souls/ Bloodborne series. 

Really like the three rune ideas though. Will 100% use those three with my 5-6 Pc's I have. I'll be sure to give credit where it's due when they come across an item with your effects. Thanks for the input and let me know if you got any other great rune ideas! Always looking for more crazy effects to add to my items and effects list!

Just so you know, I edited the post above with revamped and new ideas. Enjoy! :)

I like it. It is remeniscant of some old items. Your missing curses though. If the premise is that this armor has been kicking around for ages then at some point wouldn't someone have gotten hold of it trying to undue its effects. So a player may put it on for the first tier effect of the dex bonus to find a second tier effect of being susceptible to poison

edit. I see some curse suggestions now

Love the new additions! Thanks again!