@Tyranid Warrior
First pic: Oh gosh I remember seeing that guy's stuff in an old "bad fanart" thread on Ponychan long ago.
Second: I've heard of this one, I believe it's called "squig" (not related to the Warhammer creature). A fetish involving being impregnated with a tentacle creature. It's mostly something enjoyed by people with a combination of both pregnancy and tentacle fetishes.
Third pic: Inflation specifically of the knees? Yeah that's new even to me. Not exactly one specific part of the body I'd find all that good of a spot to inflate either in fetish art.
Fourth: All I've got is maybe it's a Disney's Planes thing, but hell if I know, I never saw that movie (wasn't interested).