Devil's Sight. Magical darkness doesn't impede the abishai's darkvision.
Magic Resistance. The abishai has advantage on saving throws against spells and other magical effects.
Reckless. At the start of its turn, the abishai can gain advantage on all melee weapon attack rolls during that turn, but attack rolls against it have advantage until the start of its next turn.

Multiattack. The abishai makes two attacks: one with its shield bash and one with its ice spear. It can replace its shield bash with a bite attack.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) piercing damage plus 9 (2d8) cold damage.

Ice Spear. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 9 (2d8) cold damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw, or for 1 minute, its speed is reduced by 10 feet; it can take either an action or a bonus action on each of its turns, not both; and it can't take reactions. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Shield Bash. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 15 (2d10 + 4) bludgeoning damage plus 4 (1d8) cold damage and the target must succeed on a DC 15 Strength saving throw or be knocked prone.

Savage Shove. In response to a melee attack roll missing it, the abishai forces the attacker to succeed on a DC 15 Strength saving throw or be knocked prone. If knocked prone, the abishai can make one bite attack against that creature.
Vicious Reprisal. In response to taking damage, the abishai makes one Bite attack against a random creature within 5 feet of it. If no creature is within reach, the abishai moves up to half its speed toward an enemy it can see, without provoking opportunity attacks.