As we have come to the conclusion that the Skulls do not in fact have adrenaline modes, I'll make some up myself:

Skull Warrior's adrenaline mode is riding its bow like a surfboard

Skull Slicer's adrenaline mode is putting a 6-stud length axle between its arms to allow it to soar majestically like a Potoo to enable it to chase after Lewa

Skull Scorpio turns its stinger into two separate wings, becoming a Skull Hornet instead of a scorpion and thus terrifying us all

Skull Basher remains the same except for the bashing function being applied to the legs, allowing it to mock Pohatu with a kick function and remind him of his old days as a G1 Mata/Nuva

Skull Grinder does nothing and consumes the mask of creation but because it's a skeleton it falls right through the nonexistent digestive system of Skull Grinder (SKELETONS DON'T HAVE ORGANS (BOTH THE BODY KIND AND THE MUSICAL KIND))

Ekimu's hammer turns into a unicycle, foreshadowing the Clown Invasion of Okoto in 2016.

As a bonus, this happened in G1. Can someone remind me when this happened? I sure don't remember it.