When Apex Altisaur enters the battlefield, its first ability triggers.
Holding priority, activate Gyome twice by paying ({2} magic symbol) and sacrificing two Foods, giving Apex Altisaur and any creature an opponent controls indestructible until end of turn.
Resolve the Apex Altisaur trigger, causing Apex Altisaur to fight the indestructible creature the opponent controls.
Apex Altisaur's second ability triggers, and Magmatic Galleon's second ability triggers if the opposing creature's toughness is less than 0.
Resolve the Magmatic Galleon trigger, if applicable, creating a Treasure artifact token.
Resolve the Apex Altisaur trigger, causing it to fight the indestructible creature the opponent controls.