This Hydra is practically unbeatable in combat because of its immunity to combat damage. That means this creature can only be killed with non-creature spells. Active effects that nullify the Ironscale Hydra's effect, such as Questing Beast's passive, may also work.
Other than that, Ironscale Hydra should go straight into Stompy lists that want a powerful creature that isn't afraid to attack and be blocked. Every time it gets blocked, the Hydra grows in size, and that can get out of hand really quickly.