That verse is so weird, a freaking low 2-C flea.
Well, this time I think that Bowser wins.
To start, and I didn't think of that in the previous match, T-Rex's intelligence is animalistic, and reptiles aren't very smart even among animals, so I'm not sure if it even will use all the abilities it has and use them correctly.
Bowser's powers and way to use them is very inconsistent, but overall he holds an advantage in mobility, intelligence, combat skill and can even kill it if it comes back as a ghost.
Bowser can resist haxes like mind manip and other powers like ice, poison and fire. Also, T-Rex's BFR seems pretty trash and not really something that makes you win.
Bowser in character can become giant, fly, alter the gravity, summon meteors, teleport and other things, he definitely has an advantage in almost everything. Reneration and immortality type 2 grant him the possibilty to endure hits and still fight for a long time. The T-Rex has unknown stamina, even comparing him to that of a real T-Rex, it wouldn't last much when fighting Bowser.
If we count all the haxes, the dino is screwed.
I think that the T-Rex holds an edge in AP, but only that.
The only wincon of the T-Rex is death manip, but we don't really know how it is used, nor if it would use it, given that is a dumb lizard.
I was forgetting Preparation time, with that Bowser can recreate the universe without the T-Rex or, more likely, put him in one of the many illusory, spatial, reality warped, black hole etc... traps that he normaly sets up for Mario and friends, winning by incap
I vote Bowser