One Piece thread (Spoilers)

and i'm even more interested in what power it is since, again, it's in the middle of slimeys gas and wasn't revealed to be a fruit until that condition happened. Very strange.

Not strange at all. Smiley "died" in this chapter. Logically It's the devil fruit he had eaten, i.e. the Sara Sara no mi Model: Axolotl.

Unless Slimey eats the fruit.

...But he had already eaten a devil fruit. Smiley (It's not slimey...) died in this chapter and became gas again.

This raises a good explanation for how blackbeard managed to ensure he got Whitebeards Devil Fruit. If when you die, the nearest fruit takes on whatever power you had upon death, that would have explained why Blackbeard needed to be the person who was closest to whitebeard, and all he would have needed is to be carrying an apple or some other fruit when he attacked him.