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You could drop hp fire/diamond storm on diancie(you already have one on mag) and adopt protect on your move set to better utilize diancie as a lead. Protect against SR users that immediately pose a threat to diancie like ferro/lando/pert/heatran(if you don't have earth power) etc. You also have...
Defenitley wait for giga drain. Without it treeko needs to wait a heck of a long time to get leaf blade. Because of its stats, treeko requires moves with general good base power. Even though Leaf blade got a big buff as it's now 90 base power, grovile's somewhat low 65 attack is nothing to write...
The thing with mega swampert is that it has a sorta FMSD. U can use hydro pump to pummel skarmory and foretress, Superpower/PuP can be used for ferrothorn, and lastly stone edge can cover gyrados. All of these pokes wall mega-swamp if he's not carrying the correct move.
Anyways, I've been...