Swarm Companion

At Level 11, you increase the beast's attribute scores by the following

STR +2, DEX +2, CON +1, WIS +1

The swarm has a number of hit dice equal to: 1d4 per trainer level

The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny rat. The swarm's attacks ignore any bonus AC provided by a shield.

When the swarm takes the Tackle action, it can use Acrobatics(Dexterity) instead of Athletics(Strength). Additionally, if a Tackle attempt is successful, it may choose to move up to 10ft and carry the target with it instead of knocking the target prone.

After the swarm hits a target with an attack, the target must succeed on a DC 14 Charisma saving throw or become frightened of the swarm for up to 1 minute. As an action, the frightened creature can repeat this save to end the effect early.

After hitting with an attack, the damage of the attack gains an additional 1d6 damage.

After the swarm hits a target with an attack, the target becomes poisoned until the end their next turn.

The swarm increases it size to Gargantuan, filling a 20ft by 20ft space. Anytime the swarm takes the Attack, Engulf, or Tackle action, it can target each creature of its choice that the swarm is sharing space with. Additionally, any friendly creatures sharing a space with the swarm gain half cover.

Melee Weapon Attack: (finesse), reach 0 ft., one target in the swarm's space. (1d4) + strength or dexterity modifier piercing damage.

1 Command Point

The swarm engulfs a target occupying the same space as the swarm, causing an incapacitating fit of panic. The target must succeed on a Wisdom saving throw DC 8 + Wisdom modifier + PB or fall prone, becoming incapacitated and unable to stand up for the duration. The swarm must concentrate on this, as if it were a spell.

At the end of each of its turns, and each time it takes damage, the target can make another Wisdom saving throw. The target has advantage on the saving throw if it's triggered by damage. On a success, the effect ends.

3 command points

The swarm may transform into an Aspect of the Flood. The swarm grows in size, expanding in a torrential wave of tiny ravenous critters. Upon transformation, the swarm gains 2d10 temporary hit points. For the duration of the transformation, the swarm cannot cling to you. The transformation lasts for 10 minutes or until the swarm chooses to revert to its normal form (no action required). The transformation ends early if the swarm drops to 0 hit points. The swarm may not use this ability again until it has finished a long rest.

2 command points

When the swarm takes damage, the swarm gains resistance to that damage. If the source of the damage also effected friendly creatures sharing a space with the swarm, they also gain resistance to that damage.