If it is Rival's Grovyle, evolve your starter a lot.
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Grovyle evoles into Torterra.
200 Pokemon is all the emerald Pokemon to get more beat elite four and get national dex
beat the 8th gym
Level 36 he evolves into Sceptile.
It is not found in the wild, you need to either trade from Ruby/Sapphire/or an other emerald, or choose Treecko as your starter pokemon, and evolve it twice, level 16 for a grovyle and level 36 for the sceptile.