Lots and lots of oran berrys and reviver seeds
You can't because as I've already said that chimchar is a sinnoh Pokemon and you can't get sinnoh Pokemon on Mystery Dungeons.
I'm not sure if it depends on the game or not, but I think you can only get Chimchar as your main-character Pokemon
get to the dark crater ther its chimchar.
Darkrai is at Miracle Sea, but you need a Secret Slab or a Mystery Part.
There will an Mystery Gift Event for Darkrai on May 9th.
lets you see darkrai in Pokemon mystery dungeon 2
wodit be better to swap chimchar for mudkip
Penis power!
its in dark crater
You have to have a naive nature.
learn flametrower for chimchar dig and have at least 3 reviever seeds and 2 stun seeds (sleep seeds don't work :( ) If turtwig learn giga drain razor leaf if can learn bullet seed and use it only on Darkrai (I deafeated Pakia in one it using bullet seed!) ~ Good luck!~
You have to beat the game to battle darkrai.