Easy way to do this is to give it the item exp share then use your stronger Pokemon to defeat trainers your wingull soon will level up and evolve.
a wingull will evolve at level 25 in Pokemon platinum, so just train it one more level for it to level up, unless you're keeping it as it is to learn moves at a faster rate.
Poochyena is a dark type of Pokemon. In Pokemon Emerald it will evolve if you raise it up to level 18.
you train them
You level a Pokemon up.
The easiest way to level up is to feed Pokemon Rare candies.
Victory road
Well you can't catch level 100 wild Pokemon in emerald, so get up and start training if you want a level 100
To get a Pokemon level up quickly is to have a Pokemon hold exp. Share and then just battle a bunch of trainers or wild Pokemon.
in elite 4.
train some electric Pokemon or just level up your Pokemon loads
your rival in Pokemon emerald has a level 18 wingull, a level 20 combusken, and one other Pokemon with a level around 20. So all you have to do is get a Pokemon that is strong against combusken and get all your Pokemon you are going to fight her with to a level close to twenty, 17 or higher, if your Pokemon is not that high yet battle trainers around slateport and in the trick master's house or fight wild Pokemon till your strong enough and remember you got to catch them all to be a master so never give up.
There really isn't much you can do with it. You can level up some other mon to lvl100