Undead Fortitude: If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the abyssal drops to 1 hit point instead.

Split Mind: The creature can split its mind doing two tasks at once (if using a spell that requires focus can only use melee attacks), also if two sides of the brain don't agree on a target for the spell it goes to a wild magic table.

Talon Slash: (1D8 + 4) + 5 to hit.

Staff Bash: (1d6 + 6) + 4 to hit.