Beastmaster

A wood elf points at the charging gnoll and a panther tackles the gnoll before choking it with its powerful jaws. A ghoul pursues a halfling through a sewer when a crocodile erupts from the depths and drags the ghoul below the water. An aarakocra waits outside a guarded tower for its flying snake companion to steal a key to the tower dungeon. Such rogues use the power a beast provides to aid in their quests.

You have bonded with a beast. It must have at least a +1 modifier to its Dexterity and have a CR no higher than CR 1/2. For example, an ape would be appropriate, but a black bear would not. You gain additional skills to supplement your companion. As your power and bond with the beast increases, the beast grows more powerful too. 

Roguish Companion

Starting at 3rd level, you gain a beast companion with at least a +1 Dexterity modifier or Stealth proficiency that is CR 1/2 or lower. Example beast companions include the ape, the panther and the flying snake. This creature adds your proficiency bonus to attack rolls, damage rolls, its Armour Class and any DC the beast possesses. It also becomes proficient in all saving throws. You can command it to Attack, Dash, Dodge, Disengage, Help or Hide without using an action. It can use your bonus actions like Cunning Action. If your beast companion is reduced to 0 hit points, it starts making death saving throws like a player character, and if it dies you can spend 25 gp worth of fine food and rare herbs to resurrect it, even if you do not possess any part of its body. It loses its Multiattack if it has one.

Bonus Proficiencies

You gain expertise in Animal Handling, Nature and Survival.

Companion's Sneaky Strike

Your companion can use Sneak Attack if it has advantage or the target has an enemy within 5 feet of it. It deals half your Sneak Attack damage, rounded up. For example, a level 7 rogue's companion would deal 2d6 sneak attack damage, as the rogue deals 4d6 sneak attack damage.

Pack Tactics

You and your beast have advantage on attacks while you are within 5 feet of each other.

Extreme Companion

Your base companion can now be a CR 2 creature with at least a +1 Dexterity modifier before the bonuses are added from Roguish Companion, like a giant elk for an elk, a saber-toothed tiger for a panther or a giant constrictor snake for a giant poisonous snake.