I honestly think DK is one of Ivysaur's easiest fights. Both play pretty similarly in the fact that they use Ftilt, Dtilt, and Bair to maintain spacing and have large grab range. Ivysaur has cool stuff going though because of Razor Leaf and Donkey Kong being a heavy makes Bullet Seed a little scarier. What I notice though is that Donkey Kong has an easier time getting the final hit in, as Fsmash is really predictable. If DK messes up his recovery he's going to eat Usmash and die, though.
I 'dunknow what's with all the Charizard being worthless, though. I'm pretty sure Charizard's grab range is equal to or greater than DK's, and Charizard has a better off-stage game with multiple jumps and Bair/Fair. I have a pretty easy time spiking DK out of his recovery. Charizard is actually pretty similar to DK on-stage, both have quick attacks for their weight-class and good range, though DK does win out in range. Donkey Kong doesn't really like Flamethrower though, and if DK misses just about any attack he'll eat Rock Smash. Charizard shouldn't try to Rock Smash around a Giant Punch though, that never works out because of the super armor.
Squirtle does terrible. Out-ranged, killed easily, has trouble killing, and has no projectile. Good. Luck.