By casting Triumph of the Hordes, you grant your entire team infect and trample, fundamentally altering how your creatures deal damage. This turns Skirk Fire Marshal's massive ten-damage board wipe into a lethal one-sided nuke, since that damage is now applied to opponents as poison counters instead of standard life loss. Meanwhile, the protective static ability of Melira, Sylvok Outcast ensures that your own creatures completely ignore the -1/-1 counter blowback of the Fire Marshal's ability, letting your Goblin army survive unscathed while instantly closing out the game.