Is It the Wild Update?

Glowfly in glass

Catch a glowfly with a Glass Bottle

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mushroom_additions:adventure/glowfly_in_a_glass

The Watch Out! Advancement is a reference to the game Zelda Ocarina.
In the game there is a fairy called "Navi" who's your "guide" in the game.
The blue little fairy, that looks like a glowfly helps you in combat and always screams "Watch Out!" while in Combat.