Hi, I love Pokémon and League of Legends and I have been working on a merge of the two for a couple of years now. These are just some ideas, and are not balanced of course!
Pokémon can be bought from the store. A player can choose a male or a female (for some Pokémon, you can only choose one gender, for example Combee, since it needs to be female to evolve) and sometimes can also choose the form of the Pokémon (for example Shellos). Pokémon all have a role in the game, which is derived from their stats (see 'Pokémon base stats + Speed stat explained') and moves.
Every Pokémon has 4 moves, all explained in the 'Pokémon moves' file. These moves may change once a Pokémon evolves. Everytime a Pokémon evolves, the player can choose what move they want on their Q-, W-, or E-slot (R-slot remains the same for most Pokémon). A player can even buy TMs to place over a slot to change a move (see 'Pokémon items'). Some moves can be an ultimate 'move' for one Pokémon, while it is a normal Q-, W- or E-move for another Pokémon. That's why only R-moves have an added effect to make it more special.
Pokémon that evolve twice, evolve always at level 6 and 12, while Pokémon that evolve once most evolve at level 9, but sometimes (for example Magikarp and Feebas) they evolve at level 6. Some Pokémon need items to evolve, which must be bought to level up. If you don't have that particular item in your inventory, you can't level up and you're stuck on the level you are now. Also, an evolutionary item may decide what evolution you are gonna get. Gloom for example can be a Vileplume with a Leaf Stone, while it can be a Bellossom with a Sun Stone.
Mega evolution happens when you buy the mega stone you need for your Pokémon. Mega stones can only be bought at level 18, and activate automatically when you go in combat.
The prices are based on the Pokémon’s catch rate (25-60=6300 IP; 75-90=4800 IP; 100-145=3150 IP; 150-220=1350 IP; 225-255=450 IP).
There are 6 different maps, each responsible for every Pokémon region. Every map contains their Legendary Pokémon (acting as Baron or Dragon in the jungle) that can be recruited for 1 minute to your team once they are killed, see 'Legendary Pokémon info'. Legendary Pokémon have a week rotation (like free champs in LoL) so that not every map always has the same Legendaries. That's because a map has too many Legendary Pokémon for a map to handle.
I think this is all introductory info I have for you now. If you have any questions, feel free to post them.