Medicham can't learn Mach Punch. It needs the raw power of High Jump Kick if it wants to succeed. Even if Medicham can learn Mach Punch, even Drain Punch is a better option:
-High Jump Kick/Drain Punch
-Zen Headbutt
-Ice Punch/Baton Pass
-Substitute
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Medichamite
Ability: Pure Power
or
-High Jump Kick
-Zen Headbutt
-Fake Out
-Ice Punch/Bullet Punch
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Medichamite
Ability: Pure Power
Medicham has a tendency to struggle against opposing Psychic Pokemon, so something to deal with them is ideal. Bisharp or Tyranitar can be the Dark Pokemon for the job; Ferrothorn, Heatran and Clefable can also deal with Lati@s. Since the 100 Speed tier is rather crowded, something to slow down faster attackers is appreciated, like Thundurus' Thunder Wave or Shuckle's Sticky Web (sure, you can use Galvantula, but Shuckle has the bulk to set up Sticky Web multiple times throughout the match):
Bisharp:
-Sucker Punch
-Iron Head
-Knock Off
-Pursuit/Swords Dance
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Black Glasses/Dread Plate/Life Orb
Ability: Defiant
Tyranitar:
-Stone Edge
-Crunch/Ice Punch
-Pursuit
-Superpower/Earthquake/Fire Blast
Nature: Jolly/Naive
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Scarf
Ability: Sand Stream
Ferrothorn:
-Stealth Rock/Spikes
-Leech Seed
-Power Whip/Protect/Thunder Wave
-Gyro Ball/Power Whip
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers
Ability: Iron Barbs
Heatran:
-Lava Plume
-Toxic
-Taunt/Earth Power/Roar
-Protect/Stealth Rock/Earth Power
Nature: Calm
EVs: 248 HP/192 SDef/68 Spe
Item: Leftovers
or
-Overheat/Fire Blast
-Flash Cannon/Hidden Power (Ice)
-Earth Power/Flamethrower
-Stone Edge/Ancient Power
Nature: Timid/Modest
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Scarf
or
-Stealth Rock
-Fire Blast
-Earth Power
-Will-o-Wisp/Stone Edge/Flash Cannon
Nature: Timid
EVs: 12 HP/252 SAtk/244 Spe
Item: Air Balloon
Clefable:
-Calm Mind
-Moonblast
-Stored Power/Flamethrower
-Soft-Boiled/Moonlight
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers/Life Orb
Ability: Magic Guard
or
-Wish
-Protect
-Moonblast
-Heal Bell/Aromatherapy/Thunder Wave
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Unaware
or
-Moonblast
-Fire Blast
-Thunder Wave
-Soft-Boiled/Moonlight
Nature: Modest
EVs: 252 HP/4 Def/252 SAtk
Item: Life Orb
Ability: Magic Guard
or
-Stealth Rock
-Moonblast
-Fire Blast
-Soft-Boiled/Moonlight
Nature: Calm
EVs: 252 HP/160 Def/96 SDef
Item: Leftovers
Ability: Magic Guard
Thundurus:
-Thunderbolt
-Hidden Power (Ice)
-Focus Blast/Psychic
-Thunder Wave
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb
Ability: Prankster
Shuckle:
-Sticky Web
-Stealth Rock
-Encore
-Infestation/Toxic/Knock Off
Nature: Bold/Impish
EVs: 248 HP/252 Def/8 SDef
Item: Mental Herb
Ability: Sturdy
