The Rat King

You reach out in front of you and sacrifice some of your residual life force to summon a series of larger-than-normal rats to swarm your foes.

This spell consumes 3 available Hit Dice in addition to the spell slot consumed. Create a number of Giant Rats equal to the total on the spent Hit Dice.

They appear one by one in the closest unoccupied space nearest to the caster within their line of sight. These rats last for the next minute or until their HP reaches 0 and each take their turn just before the caster's initiative to attack any foes within range.

You may spend an Action during your turn to compel a number of rats within 30 ft to use their next turn to perform an Interact with Object action. If the rats compelled require taking more than one Action to complete the interaction, they will Dash until within range of the object to do so.

While any Giant Rat is still alive from the result of this spell, you temporarily gain the feat Pack Tactics.

Pack Tactics. The caster has advantage on an attack roll against an enemy creature if at least one of the caster's allied Giant Rats is within 5 feet of the enemy creature and the ally isn't incapacitated.

If you do not have enough Hit Dice to meet the spell level, the spell fizzles. These rats do not count as a familiar for the purposes of casting spells from a different source.

At Higher Levels. When you cast this spell at 4th level or higher, the number of Giant Rats summoned increases by one additional Hit Dice for each level above 3rd.