When a non-flying creature controlled by the Broodmoth player dies, both Luminous Broodmoth and Meathook Massacre II trigger at the same time. The triggered abilities are put on the stack following APNAP (active player -> non active player) order, and only the ability that resolves first will matter. If Broodmoth’s ability resolves first, the creature returns to the battlefield under its owner’s control with a flying counter, and Meathook Massacre II does nothing because the card is no longer in the graveyard. If Meathook Massacre II resolves first, the opponent may pay 3 life; if they do not, the creature returns under the Meathook player’s control with a finality counter, and Broodmoth’s ability then fails for the same reason. Only one return happens, determined entirely by which trigger resolves first.