The red is a savage fighter, fury and rage and terrible power; he's also clearly enhanced by more than a few buffs from a cleric, as well as his own defensive spells, delivering his breath weapon on the beholder form, whenever he could. He shrugs off spell after spell, only growing angrier with every hit, until, finally, the disintegration beam slips through his defenses, and the dragon shudders, convulses... and is reduced to a fine, powdery ash, that explodes and scatters across a good portion of the city.