Regrettable Turn of Events
From Halopedia, the Halo wiki
The toy only appears in Remastered graphics mode. The achievement is worth 5 Gamerscore and can be unlocked on any difficulty.
The player must play with the Sputnik skull active in order to reach this toy; the Bandanna skull will also provide unlimited grenades for explosive jumping. From the start of the level make your way out of the structure, turn right, and grenade jump across the collapsed bridge. Grenade jump again up to the upper ledge of structure. From there, make your way along the walkway to the back of the structure where you will find the toy.