The bison lows angrily and presses the attack, moving around the port stairway to try and get in an attack on the new foe. Surtros slides underneath its trampling limbs, allowing the beast to take the brunt of any attacks as it moves, and places a hand on Lirith's thigh, channeling divine energy into her. "This will be your shield," he murmurs. The words are lost in the din of combat, but their intent rings clear.

Spoiler: Actions
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Bison moves to G/H 10/11, soaking up that attack of opportunity before Surtros casts his spell. It then attacks, if it can.

Attack (1d20+11)[23]
Damage (1d8+12)[16]

Casting Shield of Faith on Lirith in front of me to give her +3 to AC.

Also, can I tell who on the ship, if anyone, is below 50% health? I might as well try and combat medic it up now if this is going to be an endurance skirmish.

Heal check if necessary: (1d20+11)[14]