Are we allowed to do something like this?
[ ] Adamantine, sit on that puny plant. Roll around if he tries to dodge.
or
[ ] Sweep your tail and see how far you can bat that Bulbasaur.
If not, here's an overcomplicated plan:
[X] Attack!
-[X] Dodge any Leech Seeds and start with a quick Rock Throw. If it hits, great! If not, it'll distract Bulbasaur as we move in, maybe even mess up the terrain for him.
-[X] Strength over and over till Bulbasaur faints; don't give him time to prepare moves.
-[X] If Bulbasaur shows signs of knowing Sleep Powder, stay away and keep using Rock Throw.
At lower levels, Bulbasaur has three main threats against us: Vine Whip, Leech Seed, and Sleep Powder. Its normal and Poison attacks won't do much. Vine Whip is super-super-effective, though Onix also has over triple the defense stats compared to Bulbasaur. Leech Seed means that we can't have a prolonged battle. If it knows Sleep Powder, we can't stay at close range, though maybe a larger dose would be needed to make a giant rock snake fall asleep.
Another option is to stay away and repeatedly use Rock Throw. But that depends on Leech Seed's range.
On the plus side, Adamantine ought to be faster too.