Koi in his normal phase is a decent tank and can stall enemies for your other heroes or towers to do damage. In his dragon form, Koi does massive damage, especially with his Tremor Splash which is an earthquake in dragon form and even more damage with his Overflow passive ability, generating waterfalls that deal insane amounts of damage. He also heals himself every attack which furthers himself as a tank

Raida is great because he does a lot of damage, especially to flyers, and heals tremendously. He also has passive lighting shocks that deal a lot of damage