Rock Tomb Lure Mega Medicham
Medicham-Mega @ Medichamite
Ability: Pure Power
EVs: 252 Atk / 4SpDef / 252 Spe
Jolly/Adamant Nature
-High Jump Kick
-Zen Headbutt
-Ice Punch
-Rock Tomb
Ok, looks like a fairly standard Mega Medicham set, standard EVs, standard STABs, Ice coverage, then- what is a 60bp non-STAB move doing there? On a wallbreaker of all things??
Rock Tomb serves one role on this team- to ease prediction on forced switches. Mega Medicham's speed tier of 100, while decent, isn't fantastic, as Medicham gets outsped by a bunch of offensive Pokemon. However, it forces switches against glue mons like Clefable, Heatran, Rotom-W. When it does, the Medicham player is left with a difficult prediction, with checks like Lati@s, Gengar, and Lando-T lurking. If they pick the wrong move, they've lost all of their momentum, as Medicham gets outsped (assuming scarf on Lando) and OHKOed.
BUT
If Medicham uses Rock Tomb on the switch, it can outspeed its 'checks' and hit them with a super effective move in return. After a Rock Tomb, Jolly Medicham beats everything slower than 492 speed, including Scarfed Landorus, Scarfed Excadrill, +1 Gyarados, and Mega Alakazam. Medicham's ridiculous power allows it to OHKO these threats once given the chance.
NOTE: Adamant can be used for more power, but it only outspeeds up to 448 speed, so it loses a bit of the utility from Rock Tomb. Personally I'd go with Jolly, but it's not mandatory.