it doesnt evolve in leaf green
It doesn't, not in leaf green atleast. If you trade it to a more recent game then evolve it by happiness.
As far as I Know Chansey is not on the Pokemon Sapphire you can trade it from other versions like fire red or leaf green
its level 100
level 36.
If you have fire red or leaf green, You get the charmander for your starter pokemon, then you level it up to level 36. If you have ruby sapphire, or emerald, you trade it from Fire red of Leaf green. If you have Diamond or Pearl, you trade it from Fire red or Leaf green.
you trade it
You see Suicune level 50.
mew is not in leaf green. in emerald, it is level 30
it will be a level 26
it evolves on level 33
level 50
level 13