In the episode where Keller kidnaps Elizabeth…Neil and Keller hide in the false front of the truck, then they load the treasure, then Keller knocks out Neil. He wakes up behind the false front. Did Keller unload the whole truck, then stuff. Evil into the front, and then reload the truth, or what?

The second Neal tells Mozzie that Keller gave him the bottle and wants to play another game, Mozzie doesn't waste time asking whether Neal should do it. He asks how long Keller will be gone, then immediately starts helping him.

That's basically their entire relationship in miniature: Neal gets himself into something insane, Mozzie complains about it, and then somehow ends up helping him anyway.