Pokemon: Whimsicott
Type: Grass/Ice (Was Grass/Fairy)
Old Stats: 60 / 67 / 85 / 77 / 75 / 116 (480 BST)
New Stats: 70 (+10) / 75 (+8) / 95 (+10) / 100 (+23) / 75 / 125 (+9) (540 BST)
Abilities: Snow Warning / Regenerator / Prankster (HA)
New Moves: Ice Beam, Blizzard, Ice Shard
Removed Moves: Sunny Day, Solar Beam
Justification/Niche: Whimsicott is one of those Pokemon that I believe have been left behind, dropping off sharply after BW and its Prankster shenanigans became increasingly obsolete, despite a Fairy retyping and moveset expansion as the two generations after its introduction have passed by. This is to revitalize my ice cream ball-looking friend, turning it from a pure supporter into a supporter with the capability to attack. With STAB Giga Drain, Energy Ball, Ice Beam, and Blizzard under Hail backed by a decent 100 Special Attack, Whimsicott can quickly harrass top tier typings like Ground and Dragon, then back out with U-Turn the moment things get hairy. With Ice Shard, revenge killing becomes easier and makes spammable priority not a great option. With Snow Warning, Regenerator, and Prankster, Whimsicott can chose to either improve its supportive abilities or to become more durable. However, even with Regenerator removing Life Orb recoil and Rocks damage every switch out, a 70/95/75 defensive spread isn't getting you anywhere with a typing more crud than the stuff my dogs leave on the floor, and a 75 base Attack means Ice Shard better be hitting focus sash levels of HP.
Pokemon: Vileplume
Type: Grass/Poison
Old Stats: 75 / 80 / 85 / 100 / 90 / 50 (490 BST)
New Stats: 95 (+20) / 85 (+5) / 95 (+10) / 120 (+20) / 115 (+25) / 50 (560 BST)
Abilities: Corrosion / Merciless / Intimidate (HA)
New Moves: Focus Blast, Toxic Spikes
Removed Moves: None.
Justification/Niche: Another personal favorite, Vileplume is adorable and it's a shame nearly every single Grass/Poison in existence now outclasses it. As the original Grass/Poison that non-Bulbasaur owners could get, I believe Vileplume deserves love like Whimsicott. Retaining its good typing in Grass/Poison but receiving a stats reshuffling, you can look at new Vileplume as a slightly slower but better stats everywhere else Venusaur. With the addition of Focus Blast into its moveset, an offensive set is now feasible as it isn't hard walled by Steels like Heatran, Skarmory, and the like. With Toxic Spikes and Merciless, Vileplume can go from supportive Pokemon into offensive powerhouse, bolstering its own power while putting non-Levitaters, Poisons, Steels, and Flying types on an immediate timer. Corrosion means the middle two fear getting Toxic'd out of their invincibility, reducing their survivability against a Synthesising powerhouse. And if it wasn't scary enough, it clearly needed Intimidate for that extra fear attribute. Also to slow down Earthquakes, but that's besides the point.
All this SOUNDS good, except it's still a Vileplume. If faced down by one of the billions of Pokemon that carry super effective coverage onto Grass, like any Fire or Ice-type move, Vileplume suddenly can't outstall mons. Offensive sets lose to nearly any Special wall if it can't get its Poison spread around, but enemies also must be wary of Sleep Powder. Chansey is a generic answer but the best counter, as there's nothing it can do back. Faster Flying-types don't fear Toxic Spikes, can come in on Giga Drain or Focus Blast, and can OHKO it with nearly any STAB move since it's so slow. But it still holds a fun poisoning niche with a better offensive kit, making Vileplume, for once in its life, maybe a viable Pokemon.
I'll get to the rest in about 2 hours or so, but I'll probably be doing
Grass/Steel Forretress
Grass/Ghost Amoongus