How do you guys take down super King metal dragons?
There's a few common ways.
Leaders:
Double Dark Resist - Your leader and a friend leader with dark resist
Resist + Healer - One healer (alraune, siren the enchanter, archangel, amaterasu ohkami) and one dark resist
Odin + Healer - One odin, one healer
Zombie - Resolve team (ogre/orochi/titan + healer with low overall HP), low rate of success due to multiple monsters attacking at once
Potential subs:
Poison - Lilith/Neptune. Poison bypasses defenses, and Super King has 60000 defense (and 5000 HP). Neptune is greatly preferred since his evolved forms have a 5x poison attack, and thus should only take one or two turns to kill Supers.
Shiva - Can nullify defense, which allows you to easily take out everything. His ability pierces, so if you use it then defeat all enemies on screen, his ability will persist to the next battle and so on until you don't kill everything in one hit.
Vritra - For use with resolve teams only, get to one HP then use his ability to take out a Super in one shot
Golems - Dark/Machine golem have Armor Break which reduces enemy defense by 75%. Combining this with Odin's Gungnir ability will oneshot a Super.
I recommend using resist + auto-heal. Keep in mind that you WILL need one or more of the above subs unless you want the fight to take a million years.
