Example Beast Bondmaster 1.8 Companion: Swarm of Bats

Flyby. The swarm of bats doesn't provoke an opportunity attack when it flies out of an enemy's reach.

Harry. The Beast Bondmaster can use a bonus action to designate one creature within 5 ft. of the swarm of bats as the swarm of bats's Harry Target. Whenever the swarm of bats makes an opportunity attack against its Harry Target, if the attack hits, the Harry Target's speed is reduced to 0 until the end of the current turn. The swarm of bats will continue to Harry the target until the target dies, the swarm of bats is incapacitated, or the Beast Bondmaster uses another bonus action to change the the swarm of bats's Harry Target.

Swarm. The swarm of bats can occupy another creature's space and vice versa, and the swarm of bats can move through any opening large enough for one Tiny bat. The swarm of bats can't regain hit points or gain temporary hit points during combat, but may receive healing or spend hit dice as usual during short or long rests.

Bite. Melee Weapon Attack: +4 to hit, reach 0 ft., one creature in the swarm of bats' space. Hit: 1d6 + 4 piercing damage if the swarm of bats is at greater than 1/2 its hit points. If the swarm of bats is at half its hit points or less, the attack instead does 1d6 + 2 piercing damage.

Hounding Harry. The Beast Bondmaster can expend one Loyalty Die and use a bonus action on the Beast Bondmaster's turn to direct the swarm of bats to move in a straight line up to its speed towards its Harry Target. During this movement, the swarm of bats gains AC equal to the Loyalty Die. If the swarm of bats ends within 5 ft. of its Harry Target, it may make a melee weapon attack against the Harry Target.

Rush. The Beast Bondmaster can expend one Loyalty Die and use a bonus action on the Beast Bondmaster's turn to direct the swarm of bats to make a melee weapon attack against its Harry Target. If the attack hits, add the Loyalty Die to the damage roll, and if the target is Large or smaller, it must make a DC 13 Strength saving throw. On a failed save, the swarm of bats pushes the target 5 ft. and moves 5 ft. toward the target. This movement does not provoke attacks of opportunity. On a successful save, the next attack against the target before the start of the Beast Bondmaster's next turn has advantage.

First Wind. On your turn, you can use a bonus action to cause the swarm of bats to increase its AC by your proficiency bonus until the start of your next turn. Once the swarm of bats uses this feature, it must finish a short or long rest before it can use it again.