({6} magic symbol) ({B} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Worldfire by paying ({6} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) , exiling all permanents, all cards in all hands and graveyards, and setting each player's life total to one.
Cast Kroxa from the command zone by paying ({B} magic symbol) ({R} magic symbol) and commander tax, if applicable.
Kroxa enters the battlefield, triggering its first and second abilities.
Resolve Kroxa's second ability, causing each opponent to lose three life.
Each opponent loses the game due to having less than zero life.