Pyron in his human-sized form would have to give it his all if he's going to stand a chance against:
1. Cell (complete).
2. Majin Buu (strongest version).
3. Janemba.
4. Broly.
5. Gogeta.
6. Vegito.
Even then I doubt he'd be able to defeat the characters after 1. Majin Buu could probably warp him into something to eat or absorb Pyron and inherit his power.
Janemba can create rifts in dimensions and change form, create things out of other things (He created a sword that sliced through everything in the sword's direction) and warp whatever he sees with his mind alone, as he warped the checking station and encased King Yema and his workers in as Yema puts it "some kind of thought form". He is also able to destroy barriers between dimensions and create clones of his opponents to fight for him (He created a Goku clone out of nothing).
Broly shattered the South Galaxy as an opening feat. Whether or not that took him days to do, it's still a formidable feat that Pyron cannot do in his human-sized form.
Gogeta launched an attack that turned Janemba into dust on contact. Vegito is stronger as two people fused by potara earings would be stronger than they would be by fusing with the fusion technique. Vegito could also encase himself in a protective barrier (as shown when Super Buu attempts to absorb him and seal him in his body) that prevented Buu from trapping him and stealing his powers.