You may cast Bulbasaur without paying its mana cost if you control a card named Professor's Lab.

Absorb - {1}{G}: Bulbasaur deals 2 damage to any target. Regenerate Bulbasaur.

Evolves into Ivysaur {1}{G} (If you pay the evolves into cost, sacrifice this creature, then you may put a card named in the cost onto the battlefield without paying its mana cost)