>>528329238
The Gaster we encountered in Undertale was only a shard of a shard. For all we know he could be the same size as the ch4 titan.
I wouldn't be surprised if there's an encounter in the bunker where it seems like the ch4 titan intro, but then the wings and face form into Gaster and says
HAVE YOU BEEN LOOKING FOR ME?
HOW WONDERFUL.
I HAVE BEEN LOOKING FOR YOU AS WELL.
and ends up being an entirely benevolent titan, much to Ralsei's confusion.