When you play another Unseen, BIsma gets a random battle skill.
Entomb: Give one of your units Bisma's battle skills.
Entomb - The ability of a unit with Entomb will activate when it dies. This combines well with effects that sacrifice units as a cost.
Battle Skills - The Battle Skills are Aegis, Charge, Deadly, Double Damage, Endurance, Flying, Killer, Lifesteal, Overwhelm, Quickdraw, Reckless, Revenge, Unblockable, and Warcry.