How about something new for custom game:
Custom game is custom enough but i think this would be cool
The ability to change a pokemon's type: yes this can be changed with certain moves but since its custom game maybe changing their type could be fun too
Custom Moves: Custom moves. Kind of like a selection area for this
You put the move type (physical, special, status)
It's effects (can be effects of other moves or if its like burn paralyze etc, you put the % of it happening)
If it can miss or not, what allows it to not miss
Stats it lowers or boosts
How much PP it has
if its a move like hail or drought, what does it boost
How much damage each turn it does
if its a protect move, if it hits which effect does it apply
Move type(fire water grass etc)
Move name
Then you press Finish, and it can only exist inside custom games, only your moves can be seen and There will be a custom category displaying custom moves