Since you're using Charizard and Excadrill, you're gonna need something that's anti-water. A few good ones are Rotom-W, Vaporeon, Gastrodon, and specially defensive Celebi.
-Rotom Wash w/Chesto Berry
Nature: Bold
Ability: Levitate
EVs: 252 HP, 252 Defense, 4 Sp.Attack
Moves: Hydro Pump, Rest, Will-o-Wisp, Volt Switch/Thunderbolt
or
-Rotom Wash w/Leftovers
Nature: Calm
Ability: Levitate
EVs: 252 HP, 28 Sp.Attack, 232 Sp.Defense
Moves: Hydro Pump, Thunder Wave/Will-o-Wisp, Volt Switch/Thunderbolt, Pain Split
-Vaporeon w/Lum Berry or Leftovers
Nature: Bold
Ability: Water Absorb
EVs: 252 HP, 248 Defense, 8 Sp.Defense
Moves: Scald, Wish, Protect, Toxic/Ice Beam
-Gastrodon w/Leftovers
Nature: Relaxed/Sassy
Ability: Storm Drain
EVs: 252 HP, 252 Defense, 4 Sp.Defense
Moves: Scald, Recover, Earthquake/Earth Power, Toxic/Ice Beam
-Celebi w/Leftovers
Nature: Calm
Ability: Natural Cure
EVs: 252 HP, 232 Sp.Defense, 20 Speed
Moves: Giga Drain/Psychic, U-Turn, Recover, Thunder Wave/Perish Song/Stealth Rock
And if you need sets for Mega Zard Y and Excadrill:
-Mega Charizard Y w/ Charizardite Y
Nature: Modest/Timid
Ability: Drought
EVs: 252 Sp.Attack, 252 Speed, 4 Defense
Moves: Flamethrower/Fire Blast, Solar Beam, Dragon Pulse, Focus Blast/Air Slash
-Excadrill w/Air Balloon
Nature: Adamant/Jolly
Ability: Mold Breaker
EVs: 252 Attack, 252 Speed, 4 HP
Moves: Earthquake, Rapid Spin, Swords Dance, Rock Slide/Shadow Claw
or
-Excadrill w/Assualt Vest
Nature: Adamant
Ability: Mold Breaker
EVs: 176 HP, 52 Attack, 80 Defense, 202 Sp.Defense
Moves: Rapid Spin, Earthquake, Swrods Dance, Rock Slide/Shadow Claw