Kari Zev does not have summoning sickness and cannot be blocked and killed by an opponent.
Steps
At the beginning of your combat phase,
Helm of the Host triggers, creating a nonlegendary token copy of
Éomer with haste.
Declare
Kari Zev as an attacker.
Kari Zev triggers, creating a legendary 2/1 Ragavan creature token that is tapped and attacking.
Holding priority, activate
Goblin Bombardment by sacrificing Ragavan.
When Ragavan dies, each
Éomer that hasn't triggered this turn triggers, untapping all creatures you control and causing you to get at least one additional combat phase after this one.
Resolve the
Goblin Bombardment ability, dealing 1 damage to any target.