Ring Out!

This achievement is easy for p1 human phase and p2 bear or lynx phase.
Nothing out of the ordinary like the usual boss fight, only, group up in the middle, and make sure the three people don't move out of the grid to eat [spell=42402].

For dragonhawk, ranged spread out around the rectangle to dodge your own fire column, and keep the boss in middle to avoid having half of your group eat the same [spell=43215].

For eagle, because the vortecies pick the player position after each [spell=97647] cast, but do not move over till a second later, reposition yourself (in the rectangle) as soon as the cast is done. Totems still need to die ASAP ofc.

Also, remember to get in position beforehand and have the tank ranged pull into the rectangle instead of running up and body pull.

"Ring Out" - the name of this achievement, refers to a practice in various martial arts of either penalizing or disqualifying a combatant who leaves the arena of play (leaving a platform, a marked ring on the floor, etc.) Leaving (either by being forced out or voluntarily exiting) generally shows that your opponent has an advantage over you. In some venues (such as professional wrestling,) the ring may simply symbolize the main fighting arena, with no penalty for leaving. The goal of a "Cage" match is to eliminate the possibility for ring-out, forcing the combatants to struggle for a KO, TKO, or other victory condition.

Many arcade-style fighting games also made use of the Ring-Out mechanic, notably the Virtua Fighter series from Sega. As characters often fought on high platforms, a ring-out would often mean certain death from falling. While frustrating to some, this mechanic allowed players who were behind in a match to still win through strategic (or lucky) use of the arena edge to lure their opponents to their demise.

Step 1: Nuke the Boss
That's it, just the one step.