I'll give an example.

For the Pokemon Charmander, with the moves Scratch, Flamethrower, Smokescreen, and Dragon Breath, it'd be more like...

- Scratch
- Flamethrower (Signature - Flame Laser) A flamethrower that's heavily condensed into a powerful laser.
- Smokescreen
- Dragon Breath

Smokescreen + Dragon Breath (Dragon Smoke) - A combination move where Charmander launches a smoggy Dragon Breath that also envelops the area in blue-white dragon-charged smoke. Pokemon will take damage while inside it, on top of an initial strike.

Charmander in this case can also freely use the normal version of Flamethrower. I'm also limiting combination moves in the same moveset to 1 combination, I should probably put that somewhere.

But, combinations you make that are between two or more Pokemon has no limit.