Well here's my attempt at improving butterfree
Butterfree
Mega Stat Changes: +20 Speed +10 Special Attack -30 Attack
Ability: Chlorophyll
New Movepool Additions: Moonblast, Weather Ball, Scorching Sands
Edit: Sand is sort of like powder so i thought scorching sands could be ok
Description: I feel that having Butterfree be turned into a non-grass chlorophyll sweeper will help with its competition by turning it into more so an offensive sweeper than a support mon. With access to quiver dance, Butterfree if given the chance to set up will be able to cause serious damage to anything in its way. It now has access to Weather Ball to further abuse the sun, and scorching sands to scare off poison types. It will be a niche pick, but when used well can be very dangerous.
here's what I got for coalossal
Coalossal
Mega Stat Changes: +10 Attack, +10 Special Defence, -20 Special Attack, 1.5x weight (Due to you, know, the mountain of coal)
Ability: Steam Locomotion (The name's not the best but it'll do) works like steam engine, but gives a water immunity along with the speed buff.
New Movepool Additions: Wild Charge
Description: Coalossal will be a switch in on water type threats, threatening them with blisteringly fast speed (after the steam locomotion boost), still packing It's great bulk and now Wild Charge. This allows Coalossal to play a part in defensive play while still threatening offense. With It's new weight buff, Heat Crash and Heavy Slam become more useful, giving Coalossal more options.
And finally Centiskorch
Pokemon: Centiskorch
Mega Stat Changes: +5 Attack, +15 Speed, -20 Special Attack
Ability: Hustle
New Movepool Additions: U-Turn, Earthquake
Description: With It's new coverage and ability, Centiskorch becomes a real offensive threat, and no longer needs its special attack. U-Turn is great to keep momentum, and earthquake is a great addition to its movepool. Sort of like a slower but more powerful fire type durant.