how good is typhlosion?

Use for fun, not because its really that useful. Flareon, Arcanine, Charizard all better unfortunately.

I cannot answer this question without hurting your feelings so here is a balloon.

It is a charizard that doesn't fly and has worse moves, unfortunately.

However, the worse case scenario (solar beam) is far superior to chariard's worse case scenario (dragon claw)

It has a charge move that covers al of its weaknesses, which is currently undervalued due to the current gym system in Pokémon Go but it will work as a wild card when PvP is released

Unlike Charizard it doesn't have double weakness to rocks. And it's fatter than Flareon. Better defender than either, and I hope Fire types would be relevant for defense someday. I'm all for diversity. Arcanine might be better but its moves are meh, at least in my K9 squad, no double fire ever.

I caught one with shadow claw/over heat. Level 29 low ivs. It's definitely fun to use especially with that moveset. But yeah in terms of pure performance it's behind Flareon and Arcanine in my experience and I don't really have a Charizard to compare it with.