Borrowed time. When abaddon reaches 25 or below hit points he instead remains at 25. He is then surrounded by an other worldly blue glow until the end of his next turn. During this time any damage inflicted to him is instead healing him.

Multi attack. Abaddon can make two melle attacks.

Runeblade. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 12 (2d8+3) [slashing] damage plus 5(1d10) cold damage. If the target is a living creature it must make a DC 15 constitution saving throw or have its speed reduced by half until the end of the next turn.

Aphothic shield (Recharge 5-6). Abaddon summons an unnatural barrier around a creature he can see within 40ft. The creature gains 15 temporary hit points that last for 1 minute. When the effect expires or the temporary hit points are depleted, the shield explodes in a wave of unholy energy. All creatures within 10 ft must make a dex DC 15 saving throw taking 18(4d8) force damage on a failed save or half on a successful one.