With Charizard, I usually go for the grab first thing or act like I'm about to go for the grab and use Flamethrower followed by a grab instead. If there's platforms and I see the enemy go up, I usually approach with fair and sometimes nair or Rock Smash. Sometimes if you fast fall Charizard's aerials, it sets him up nicely for an ftilt. Then if I just want the enemy to back off me, I usually go with upsmash.
With Squirtle, I start off Shell Shifting to see how the enemy reacts. Then I'll go with fair, bair, or nair or I'll go for the grab.
With Ivysaur, I usually throw Razor Leaf once to see how the opponent reacts. If they shield, I'll usually go for a grab. Most times I go for a nair, though, followed by utilt or ftilt; if the enemy is a heavy, I'll aim to fastfall nair to a Bullet Seed. Sometimes I catch the enemy off-guard on a stage with platforms, and Ivysaur can actually land a surprise KO with nair to upsmash. Of course if the enemy is behind Ivysaur, bair wall for the win.