so the beast master has an reputation for being particularly weak, but i think i have come up with a few tricks for making the most out of this, as well as a few of the best beast companions i have been able to find.

thing to keep in mind: beast master pets gain hit points slowly, only having an amount equal to four times your ranger level, about the same rate as a wizard. This amiunt replaces all pre existing hit points, so having more hit points is not always a good thing. You add your proficiency bonus on top of the beasts proficiency bonus to skills the beast is proficient in and to the to hit bonus of their attacks, as well they get an bonus to armor class and all damage rolls equal to your proficiency bonus.

purchase barding: barding is armor made specifically for an animal, an costs four times the price of the normal armor set, and since your beast has so few hit points making shure they never get hit is going to be an priority. If people do not sell the armor you are looking for, use the crafting rules to make some. My recommendations for armor is as follows: If your animal companion has an dexterity score of 18 or higher, buy some studded leather barding for 180 gold pieces. If your companion has an dexterity score of 11 or less, buy ring mail armor for only 120 gold pieces or chain mail for 300 gold pices, if your animal companion has some other dexterity score, buy some scale mail or an chain shirt for 200

giant poisonous snake my first example of an beast, this one has an mighty bite that deals 1d4 + 4 piercing damage without aid from an friendly beast master, and the victim must make an DC 11 constiruion saving throw or take 3d6 poison damage, or half as much on a sucessful save. This is an great companion to have if you want your companion to deal a lot of damage since you get to add your proficency bonus to the damage of the bite itself and your proficency bonus to the damage the bite cuases, and since the giant poisonous snake has such high dexterity its bonus to hit at level 3 when you get it should be +8, more accurate than anything else, assuming your damage does not fall behind the dynamic duo of snake and ranger can collectively have an damage per second much higher than that of any other class, like assuming no resistance is at play the giant poisonous snake will do more damage with its bite attack than any non-rouge character can make with a single weapon attack, even if the target succeeds on its DC 11 con save

the deep rothé is an strange beast, it is an variant of the cow stat block found in volo's guide to monsters, and it is an type of cow that is much smaller than others, lives underground and has magical flashing lights. in game terms this means it has an size of medium instead of large, is able to innately cast dancing lights, has darkvision and is able to communicate using "magical flashing lights" with other rothé. Since communicating using magical dancing lights is listed as an language in the stat block on dnd beyond, it stands to reason that somebody might learn to understand this strange way of communication, and if you are able to cast dancing lights you might be able to communicate with it in an meaningful manner yourself. To make the most out of this strange companion, make shure to play as an drow, and to pick the merchant background, with deep rothé as the language gained by your background, since then you are also able to put an cart onto this cow that is too small to ride.

other than being really cool and being able to cast cantrips, the deep rothé is also able to make an gore attack for 1d6 + 4 damage, that is not bad at all when taking into consideration that you add proficency to damage and you get to deal an extra 2d6 damage if your disco themed cow moves 20 ft beforehand, it is not bad at all

Pteranodon an flying "dinosaur" that is technically not a dinosaur, it is an medium creature with an 60ft flying speed that does not trigger opportunity attacks, if your characters size is small you combine this with an lance, an shield and the dueling fighting style to make yourself the kind of the skies, able to fly high into the sky with you mounted on it and make devestating attacks. Yes to even ride one you need to purchase an exotic saddle for 60 gp but that is an worthwhile investment for what is more or less an permanent fly spell cast on you, its bite attack is still not verry good at all, so keep to making all the attacks yourself and let you do the flying, might even be worth mounted combatant

giant wolf spider an really spooky companion, not nice to bring to the table if your friends have arachnophobia, but let us ignore that and look at its stats and particular benefits: Its bonus to stealth checks, +7, is the highest of any beast that is viable for your companionship, and you add your proficency bonus on top of that so that spider is going to run arround with an +9 to its stealth checks while y'all are still level 3. It also has an decent +3 to perception that will once more be buffed by your proficency bonus. Furthermore, it has spider climb to help with mobillity, an really terrifying 40 ft normal and climbing speed, it has 10 ft of blindsight so it can fight effectively against invisible opponents or in total darkness, its bite has an weak to hit bonus and deals nowhere near the same damage as the terrifying giant snake, it still deals some decent damage and once again its attack is split up into two separate damage rolls so you get to add your proficency bonus twice to damage

giant frog: the benefit of the frog is suprisingly enough its abillity for debuffs/support, let me explain. Oppon hitting an target with its bite attack, the target automatically becomes restrained and grappeled by the frog, for the duration of this grapple the frog can make bite attacks only against the target and the target must waste its action if it wants to try to escape. (An restrained target has disadvantage on all attack rolls and all dexterity saving throws, its speed is zero and all attacks against it have advantage, so this good froggo of yours can grant free advantage on your allies attacks and force the enemy to waste its turn). Furthermore, the frog can swallow an small or smaller creature it is grappling to swallow it, dealing automatic acid damage to the swallowed target and making it both blinded and restrained. And beyond that the frog is simply great for the interaction / exploration pillars of the game, since it can jump over almost any gap with ease, breathe underwater and it also has an innate swiming speed, it has good mobillity and it can support the party, what more could you possibly want?

fastieth an creature from ebberon: rising from the last war that was probably designed with the beast master ranger in mind, it has really really high dexterity, an 50 ft movement speed and it an occasionally take the doge action as an bonus action (i dont think you need your action to command your companion to take an bonus action, they just can do it), their attack has an +6 bonus to attack (plus your proficency bonus so +8 in total at level 3 and increasing as you go along) and it deals an pretty decent 1d8 + 4 damage, 1d8 + 6 at 3rd level, an number that should keep up pretty decent with the damage of your weapon attacks and the attacks of any paladins or fighters in the party, it has low hit points but that does not really matter due to how ranger works

Other thing I'll add, is that the HP replaement feature of a Beast Master means even very small low challenge rating beasts like Owl, Spider, or Stirge can be made "tanky" enough to function as a combatant (especially with a +2-6 proficiency bonus being added to their AC). The Beast Master adds their proficiency bonus as a static modifier to the Beast's attacks, so even very low damage die attacks (or attacks that do only 1 damage!) can get bumped up to do meaningful damage (though I don't believe any of them will ever be good when compared to a different character optimizing their own attacks).

Personally I feel like turning a Wolf into a slightly better Wolf feels like a snooze fest, but creating a jacked up bug like a Stirge with AC 16-20, 4-80 HP, which bites for 7-11 and then does 7-11 on  the start of its subsequent rounds even when you don't command it is pretty nifty for a Beast Master that struggles with action economy :)

honorable mention goes to giant lizard, who with the two optional traits is super useful out of combat, cave badgers from out of the abyss who have tremorsense and can dig 15 ft per round, the dimetridon deals the most per hit damage without using poison and can easily outclass an fighter using an greatsword in terms of damage dealt, but has nothing special other than that, as well as swarms and blink dogs who would have made it if they were at all legal

Is the beast master ranger still weak if you apply to sidekicks UA template to your beast companion?

Quote from Chicken_Champ >>

Other thing I'll add, is that the HP replaement feature of a Beast Master means even very small low challenge rating beasts like Owl, Spider, or Stirge can be made "tanky" enough to function as a combatant (especially with a +2-6 proficiency bonus being added to their AC). The Beast Master adds their proficiency bonus as a static modifier to the Beast's attacks, so even very low damage die attacks (or attacks that do only 1 damage!) can get bumped up to do meaningful damage (though I don't believe any of them will ever be good when compared to a different character optimizing their own attacks).

Personally I feel like turning a Wolf into a slightly better Wolf feels like a snooze fest, but creating a jacked up bug like a Stirge with AC 16-20, 4-80 HP, which bites for 7-11 and then does 7-11 on  the start of its subsequent rounds even when you don't command it is pretty nifty for a Beast Master that struggles with action economy :)

 that is really really cool, forgot about the stirge, problem is that it sucks an set amount of damage before it detaches, but i guess that is more to do with natural behavior and might be able to be trained away, and it is less useful when you reach 11th level and your pet needs to attack twice to keep up but cannot becuase it must succ that goblin juice

Quote from TexasDevin >>

Is the beast master ranger still weak if you apply to sidekicks UA template to your beast companion?

 were you even paying attention to what i was saying during the post? the sidekicks was nerfed massively since they were approaching to close to the power of characters when they officially released them in the starter kit, getting to increase hit dice and abillity scores at the same time as you add your own proficency bonus to everything? and the companions own profiency bonus increases on top of that, so the companion basically has expertise in attack rolls and their abillity scores start at an higher level as the players already like unless you just ignore the subclass entirely and just give the ranger a diffrent subclass or nerf the base beast master you will just have an ridiclus monster on your hands like seriously what are you thinking?

Mage Armor considerably improves any of your pet’s AC.  Also try Warding Bond for good shenanigans.

At level 15 strongly consider branching out to a Spellcaster class that combines well with Share Spells.  There are some really good combinations.

Also, don’t attack with your Pet and don’t command it so it auto-dodges. Use it for opp-attacks to lockdown the battlefield.  Only attack when you really have no other option.

Also, use flyby if you want to use the Help option with your Pet.  Give yourself free advantage once a round will be helpful and Flyby will keep your pet more relatively safe.

Maneuver your Pet on the FAR side of the enemy away from the rest of the party. Keep it squarely away from AoE attacks. 

Quote from ArtificeMeal >>

 were you even paying attention to what i was saying during the post? the sidekicks was nerfed massively since they were approaching to close to the power of characters when they officially released them in the starter kit, getting to increase hit dice and abillity scores at the same time as you add your own proficency bonus to everything? and the companions own profiency bonus increases on top of that, so the companion basically has expertise in attack rolls and their abillity scores start at an higher level as the players already like unless you just ignore the subclass entirely and just give the ranger a diffrent subclass or nerf the base beast master you will just have an ridiclus monster on your hands like seriously what are you thinking?

I'm sorry man, I just read this paragraph several times and I still have no idea what you are trying to tell me. It sounds like you are complaining that the sidekicks system was nerfed and at the same time explaining that it makes companions overpowered. I thought your intention was to maximize the beast master.

Nonetheless, thank you for the kind words.

Quote from TexasDevin >>

Quote from ArtificeMeal >>

 were you even paying attention to what i was saying during the post? the sidekicks was nerfed massively since they were approaching to close to the power of characters when they officially released them in the starter kit, getting to increase hit dice and abillity scores at the same time as you add your own proficency bonus to everything? and the companions own profiency bonus increases on top of that, so the companion basically has expertise in attack rolls and their abillity scores start at an higher level as the players already like unless you just ignore the subclass entirely and just give the ranger a diffrent subclass or nerf the base beast master you will just have an ridiclus monster on your hands like seriously what are you thinking?

I'm sorry man, I just read this paragraph several times and I still have no idea what you are trying to tell me. It sounds like you are complaining that the sidekicks system was nerfed and at the same time explaining that it makes companions overpowered. I thought your intention was to maximize the beast master.

Nonetheless, thank you for the kind words.

 okay, let me explain this in a simpler (and kinder) manner:
the "new" rules for sidekicks only lets you have humanoid sidekicks, so if you want one you will have to use the unearthed arcana rules.

the beast master subclass increases your beasties armor class, its damage and its bonus to hit as your proficency bonus increases. This feature also "stacks" with the proficiency bonus of the beast itself, so an level 3 ranger will have an proficency bonus of +2, and his beast will have a proficency bonus of +2, so its bonus to attack could be like +7 at level three if the beast has an abillity score of 16 in their attacking stat. Normally, the beasts own proficency bonus never increases, but yours do.

if we add the sidekick rules on top of this, the companion will grow and your little baby will grow fast, his or her proficency bonus will now increase every level, this means that every skill your companion was proficient in it now basically has expertise in as it adds your proficency bonus to its own skill checks, and certain beasts like the giant wolf spider and the panther has expertise in its own skills, so now it gets to add twice its own profiency bonus plus your profiency bonus. This phenomenon also means that the beast companion will have "expertise" in attack rolls as well. The beast also gains abillity score improvements, something they dont normally do that also stacks with all of this other nonsense, as long as their primary attack is even close to decent you will soon outclass every barbarian and fighter in your party in terms of per attack damage, and the 5th level feature means that you get the 11th level feature at level 5, since you can command the beast to make two attacks and then make one attack yourself.

i get what you are trying to say, the beast companion falls a little short, and this can be fixed by just giving the ranger an CR 1/4th animal companion and then letting them pick an completely diffrent subclass,  or by changing what the beast master does to its companion exactly, just keep in mind that you cannot have your cake and eat it, having both the subclass and giving your companion npc class levels will just lead to ridiculous shenanigans

I was unaware that they had revised the sidekick rules to only allow for humanoid sidekicks. Thanks for pointing it out. It really makes my whole question irrelevant in the context of the beast master, which explains why you said so. In which publication did they do this?

Quote from TexasDevin >>

I was unaware that they had revised the sidekick rules to only allow for humanoid sidekicks. Thanks for pointing it out. It really makes my whole question irrelevant in the context of the beast master, which explains why you said so. In which publication did they do this?

 in an set called the "dnd essentials kit", the rules are provided in an appendix, rules for levels above 6 must be found within another box set that i dont know the name of, think of it as "the starter set, but better".

D&D Essentials kit isn't available on D&D Beyond, but Icespire Peak is. I took a look and I see the sidekicks offered there. I feel like stuff set out in an adventure module isn't' really meant to be rules so much as material intended to be relevant to that adventure. I would have never thought to take the examples they gave as rules meant to apply across the board. For one thing, they stop at level six. I think it's perfectly valid to say "The sidekicks material is UA so I don't want to use it" but I'm not sure the material in Icespire Peak makes the UA sidekicks material any less valid.

Quote from TexasDevin >>

D&D Essentials kit isn't available on D&D Beyond, but Icespire Peak is. I took a look and I see the sidekicks offered there. I feel like stuff set out in an adventure module isn't' really meant to be rules so much as material intended to be relevant to that adventure. I would have never thought to take the examples they gave as rules meant to apply across the board. For one thing, they stop at level six. I think it's perfectly valid to say "The sidekicks material is UA so I don't want to use it" but I'm not sure the material in Icespire Peak makes the UA sidekicks material any less valid.

 i dont actiually own the book, i just kinda know it from people who do, but the two sequel modules provide rules for progressing above 6th level if you are really curious (yes the spell caster finally gets treated as an full spell caster by then instead of having spell slots like an artificer), but from the designers point of view, i think they do consider these rules to be the successor to the unearthed arcana article, and that is kinda sad, but who knows, maybe an third iteration of the sidekick rules will be released, perhaps officially this time

Quote from ArtificeMeal >>

honorable mention goes to giant lizard, who with the two optional traits is super useful out of combat, cave badgers from out of the abyss who have tremorsense and can dig 15 ft per round, the dimetridon deals the most per hit damage without using poison and can easily outclass an fighter using an greatsword in terms of damage dealt, but has nothing special other than that, as well as swarms and blink dogs who would have made it if they were at all legal

Giant lizard is large in size. Don't know about cave badger, but giant badger is good.

Quote from KaoshiElder29 >>

Quote from ArtificeMeal >>

honorable mention goes to giant lizard, who with the two optional traits is super useful out of combat, cave badgers from out of the abyss who have tremorsense and can dig 15 ft per round, the dimetridon deals the most per hit damage without using poison and can easily outclass an fighter using an greatsword in terms of damage dealt, but has nothing special other than that, as well as swarms and blink dogs who would have made it if they were at all legal

Giant lizard is large in size. Don't know about cave badger, but giant badger is good.

 cave badger is an variant of the giant badger found in "out of the abyss", and **** you are right, we cannot have cool lizard, 

Maybe ask DM. Some may say ok...

What magic items would make them better?

Insignia of Claws?

Quote from LeviRocks >>

What magic items would make them better?

Insignia of Claws?

 obiously any magical armor will help a lot, demon armor perhaps for buffed unarmed damage?

other than that wearing the ioun stone of mastery gives your companion a +1 to hit, to damage, to armor class, all skills they ar proficent in, making them just better at everything they were already good at, proficency bonus for the beast master ranger is super important, any magic item that increases it is powerful, as it increases both your own power and the power of your companion, yes it is ledgendary but it is also an better version of insignia of claws in this instance, even if the insignia will be more available

maybe if you have the awaken spell on and your companion is a giant crab or something who can hold stuff, the shield of missile attraction or maybe even an actual weapon?

You have to be careful with magic items that require a special activation, because "Use an Object" is not one of the commands that you can give an animal companion RAW. There was a thread a while back about maximizing the iron defender companion to the artificer where I came up with a list of items that a companion might wield to effect without having to actively uncork any bottles, but don't have the link handy... just keep it in mind. 

I'd like to point out that Giant Poisonous Snake probably does the most damage. It's my favorite Beast Master Companion of all time.