Question

What is the best strategy to kill Mr. Punish? It is possible to kill solo with a Mage 290?

Answer 1

Will all come down to killing solo or with team.

Team - clear prior rooms, depending on level of team. Knight/Paladin blocking can easily tank boss with other monsters.
Solo - due to respawn of rooms, if high enough level. Run to 4th room (room before throne) or hallway (before throne). Will need to clear monsters around hallway. Can use energy bombs to help offset the amount of monsters.

Regardless of team or solo, please be advised it is immune to ice damage. Using Ava or ice ue will not work but can offset the amount of monsters around. Other wise single target with SD runes.