Summon Aberration

You call forth an aberrant spirit. It manifests in an unoccupied space that you can see within range and uses the Aberrant Spirit stat block. When you cast the spell, choose Beholderkin, Mind Flayer, or Slaad. The creature resembles an Aberration of that kind, which determines certain details in its stat block. The creature disappears when it drops to 0 Hit Points or when the spell ends.

The creature is an ally to you and your allies. In combat, it shares your Initiative count, but it takes its turn immediately after yours. It obeys your verbal commands (no action required by you). If you don’t issue any, it takes the Dodge action and uses its movement to avoid danger.

Using a Higher-Level Spell Slot. Use the spell slot’s level for the spell’s level in the stat block.

In addition to the noted usage of the spell's level in the spirit's Traits and Actions, the following attributes are also affected.

Aberrant SpiritAC11 + the spell’s levelHP40 + 10 for each spell level above 4Speed30 ft.; Fly 30 ft. (hover; Beholderkin only)PBequals your Proficiency Bonus