I know see though that this is a bad idea mainly because it would take away the advantage people would go with by using fast or slow pokemon.
This Is an example of where a donphan could move to with its 4 tile range, thats being able to move 4 tiles without going diagonally.
Green is normal Grass/Ground
Brown is anyground higher then the green tiles ie any tile higher then normal level
purple is where donphan is standing
yellow is where it can move to