Monstrous isn't an ability that a creature has. It's just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.
Polis Crusher
An ability that triggers when a creature becomes monstrous won't trigger if that creature isn't on the battlefield when its monstrosity ability resolves.
“Protection from enchantments” means that Polis Crusher can't be enchanted, it can't be targeted by Aura spells or by abilities of enchantments, all damage that would be dealt to it by enchantments is prevented, and it can't be blocked by enchantment creatures. Notably, it doesn't have protection from enchanted creatures (unless those creatures are also enchantments).
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Chase Stone
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
