Y, you ask (yea, corny, I know)?
Drought: No water weakness per se, for 5 turns
Drought: A single Sun-boosted Fire Blast can cause massive damage, even to Water types.
Drought: Single Turn Solar Beam
High Offensive Stats: Basically like a Glass Cannon post Stealth Rock Damage, with that speed and Special Attack, Charizard Y can break through an unprepared team
Resistance to Fairy type moves: [*Creds to Astro, who for some reason didn't answer :P]*
Stealth Rock: Eh, who cares, with this beast, it doesn't matter all that much. Seriously, once this guy is in play, it's kind of hard to get rid of him.
4x Rock, 2x Electric: Both coverable by the movepool, tbh. Either way, Charizard, in this fast pace meta-game is kind of frail, anyway.