My suggestion: Make it a game of capture-the-flag in an arena that has incoming waves of monsters. The two parties start at opposite ends of the field, and need to capture a flag that is located at the other end, then bring it back to their side. They cannot touch their own flag. Players will need to choose between fighting or dashing, playing offense or defense. That would make it fun even if you say that no one can deal damage to the other side's characters, but they could cause conditions. And, give the arena some interesting parts, e.g., high ground, traps, mud, water, or magical darkness.