He can't beat pretaunt, and he gets shut down by prebuffs like zaul stealth
His ability should be in effect before even leader abilities are in effect. Otherwise technically he isn't shooting first, he's "shooting after"
This singular buff would make him viable.
After all the responses, this is the best idea for a zeta of his unique
his zeta ability should be as follows:
Han has +25% critical chance. Han takes a bonus turn before each encounter starts and any buffs are applied, where he can use his basic ability and stun his target. this attack cannot be evaded. In addition, whenever han is targeted by a single-target attack, he has a 50% chance to attack the enemy first with his basic and 30% critical damage, with a 50% chance to stun the target for that turn only.