Thanks for your advices guys. I'll think I'll go with Dragon Pulse for Lucario in case some dragon takes down my Gardevoir.
Vinny, how do you get Roost on your Crobat ? I thought such TM wasn't implemented yet.
Gyarados doesn't appeal to me, his movepool is currently too useless to help, I think (Draco Dance sounds nice but he'd add a Rock weakness to the team and would only bring water-type move, because Mamoswine already learns Ice Fang).
Azumarill wouldn't disturb the team's balance but he'd only bring a water-type move, just like Gyara, wouldn't he ? What movepool would you suggest ?
I think the only type which could cause me trouble is currently Fire (no real counter actually, even if Mamoswine's Thic Fat would help him placing Earthquake). Therefore, I'd need a water or dragon type Pokemon..
Flygon sounds good, learns good moves even in Reborn, but.. Aaargh, I don't know. Strategy with half the Pokemon & only a few TMs is too damn hard !