In addition to the above comment, pokemmo uses movepools from gen 8 (meaning pokemon can learn moves they could not in the OG games) as well as updated base stats and abilities for a few pokemon.
Said moves and abilities act like their modern counterparts too. (Weather isn't eternal, rapid spin gives +1 speed, those kind of things)
Not all hidden abilities are available either, we're currently in the process of them being added to the game.
And a few nerfs are in place, Baton pass doesnt pass stat changes, Garchomp doesn't have access to Swords Dance and Hydreigon can't learn Draco Meteor.