Curse is a terrible move to use on Crobat, even if you have White Herb to negate the Speed drop. Given the one-shot nature of your current set and Crobat's terrible offensive move pool, it's not a very good setup attacker. Crobat's best role is a supporting stall breaker, though its stats may not scream that role. Its defensive typing is good, which is why it's generally seen in that role:
-Brave Bird/Acrobatics
-U-turn/Toxic/Taunt
-Defog/Taunt
-Roost
Nature: Jolly
EVs: 248 HP/60 Def/200 Spe
Item: Black Sludge/none
Ability: Infiltrator
However, Crobat has (barely) enough offensive moves to string together a Choice Band set:
-Brave Bird
-U-turn
-Cross Poison/Defog
-Sleep Talk/Defog
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band
Ability: Infiltrator
What purpose does your EV spread for Heat Rotom serve? Heat Rotom needs max Special Attack and max Speed to make the most out of its Choice item. It also needs a Timid nature to outspeed as many things as possible, especially walls, so it can chunk them hard with Specs-boosted attacks. And speaking of Specs, it's the best item to use with Heat Rotom, turning its Overheats into nukes. Tl;dr:
-Volt Switch
-Overheat
-Hidden Power (Ice/Grass)/Thunderbolt
-Trick
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Specs
Heracross shouldn't run Brick Break. At all. That move has significantly less power than Close Combat. The defensive drops don't matter, as Guts Heracross is meant to be a hit-and-run attacker:
-Swords Dance
-Megahorn/Facade
-Close Combat
-Knock Off
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Leftovers/Flame Orb
Ability: Guts
Heracross can also run Choice sets effectively:
-Megahorn
-Close Combat
-Knock Off
-Stone Edge/Earthquake
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band/Choice Scarf
Ability: Guts/Moxie
Bulk Up Chesnaught seems tempting, but it's better off in the general support role department, as it has a somewhat bad case of 4-moveslot syndrome, a situation when a Pokemon learns a lot of good moves, but can't fit them in all in 4 moveslots . And speaking of Bulk Up users in general, they must run a Careful nature with 252 HP/4 Def/252 SDef, as their Special Defense isn't being boosted by Bulk Up; without that kind of investment, special attackers have a field day with them:
-Spikes
-Leech Seed/Synthesis
-Spiky Shield/Roar
-Drain Punch/Wood Hammer
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Bulletproof
Mega Blastoise is best played as an offensive Rapid Spinner. This is very crucial, as both Heat Rotom and Crobat are weak to Stealth Rock. It seems tempting to use Aqua Ring as a Leftovers substitute, but it's pretty much a wasted moveslot, as Mega Blastoise has good offensive coverage, and you're wasting that:
-Hydro Pump/Scald/Water Pulse
-Dark Pulse
-Aura Sphere/Ice Beam/Dragon Pulse
-Rapid Spin
Nature: Modest
EVs: 252 HP/252 SAtk/4 SDef
Item: Blastoisinite
Since Blastoise is your offensive Spinner now, I think you need a Wish user on this team, preferably over Cloyster, as Blastoise lacks reliable recovery and your other attackers can get worn down throughout the battle. Florges and Umbreon are the best Wish-passers in UU:
Florges:
-Wish
-Protect
-Moonblast
-Aromatherapy/Toxic
Nature: Calm
EVs: 252 HP/232 Def/24 SDef
Item: Leftovers
Umbreon:
-Wish
-Protect
-Foul Play
-Heal Bell/Toxic
Nature: Calm
EVs: 252 HP/4 Def/252 SDef
Item: Leftovers
Ability: Synchronize