Blood Construct

Blood Form. The construct can enter a hostile creature's space and stop there.  It can move through a space as narrow as 1 inch, without squeezing.

Multiattack. The construct makes a number of slam attacks equal to half this spell's level (rounded down).

Slam. Melee Weapon Attack: + (your spell attack modifier) to hit, reach 5 ft., one target. Hit:  1d6 + 3 + (the spell's level) bludgeoning damage +1d6 force damage.

Drowning in Blood. Recharge (5-6) Whenever the construct enters a medium or smaller creature's space, the creature must make a Dexterity saving throw using your spell save DC.  

On a successful save, the creature can choose to be pushed 5 ft. back or to the side of the cube, not provoking opportunity attacks.  

On a failed save, the creature takes 10 (3d6) force damage as it is constricted.  The engulfed creature can't breathe and is restrained.  At the start of each of the cube's turns, the creature takes an additional 10 (3d6) force damage.  When the construct moves, the creature moves with it but the construct has it's movement slowed by 10 ft.  Only one creature can be drowning in blood at a time.

A creature who is drowning in blood can try to escape by taking an action to make a DC 15 Strength check.