@Flightmare_rider suggested a Gaster and Tony Stark crossover. That's... not exactly what happened, but here, have this.

Gaster: "What are you guys watching?"
Sans: "movie called 'iron man'."
Gaster: "...hm."

LATER,

Sans: "hey, dad. what'cha workin' on?"
Gaster: *no response*

Sans: *looks at blueprints*

Sans: ...

Sans: *facepalm* "dad, no."
Undyne: "DR. GASTER YES."

For the record, I really hate drawing robotic/mechanical things, but this was just too good to pass up.