I Choose You, Steelbreaker (25 player)

Obviously a reference to "Pokemon". Whenever a trainer would send out a pokemon, they would say "I choose you <name>!"

I found it pretty funny. :)

Killing a boss of the Iron Council Supercharges the remaining bosses, healing them to full, increasing their damage and giving them new abilities. To get this achievement, Steelbreaker must be killed last. Since his abilities are most dangerous, this is considered to be the hard mode of the encounter.

Steelbreaker starts off with the High Voltage and Fusion Punch abilities.
When 1 other boss is killed, he can cast Static Disruption, an AoE and nature vulnerability spell.
When both other bosses are killed, he will debuff his current target with Overwhelming Power, increasing that players damage but causing a Meltdown, killing that player after 25 seconds. Spare tanks are advised. Once both other bosses are killed, Steelbreaker also gains a stacking +25% damage buff and 15% HP heal for each player he killed (including Meltdown casualties).

Steelbreaker is the most difficult 'Final' boss of Iron Council - as you kill each of the three, the others are healed to full and gain extra skills, the third one alive being a dangerous boss on its own.