Is synergy the new trend in metal? Arguable kings of the genre, Mastodon, have joined with Dethklok -- the real-life version of the animated band from the Adult Swim show Metalocalypse -- as co-headliners on a 34-city tour sponsored by the offbeat TV network. Toss in earnest math-metal quartet Converge and intense stoner-metal band High On Fire, and the formidable lineup and sheer volume are enough to drown out any naysayers. Or are they? As one conflicted Lynyrd Skynyrd-hoodie clad teen predicted before the show, "It's gonna be a bunch of Adult Swim kids getting their asses kicked." Not exactly.