Sorry for posting so much on your profile page, but I get a lot of ideas, and right now I just made this account, and Smogon wont allow me to reply to threads, so this is another core idea: Manaphy + Seperior
Serperior should switch in when a grass type or electric types threatens Manaphy. It will have; glare (for the grass types, that will most likely switch out), substitute (if a grass or electric type stays in), Leaf storm (Main attack that serves as a nasty plot, and hits hard), Synthesis (for recovery) A good teammate would be a bulky wish passer. or a mega manetrik to absorb electric type attacks.
Manaphy, and Serperior cover each others weakness's, and both set up faster then all the other Mons. Manaphy can either be specially defensive, or specially offensive, with tail glow, scald, (For physical attackers, and stab, and rocks/fires/grounds) energy ball, (for Quagsires, and water types) ice beam (for flying types). Serperior should have Spd, Sp. def, or sp. attk
Also a sp. wall Gardevoir is quite unexpected, but its actually very bulky, and still hits hard. (Im posting this here, because I just created this account, and Smogon isn't letting me reply to threads for some reason).
I think a 252 Hp/252 Sp. Def Wish/protect Gardevoir with heal bell, and hyper voice combined with a scarf trap/volturn Magnezone would be a great core. Magnezone completely destroys iron types that always switch in on Gardevoir.