(You can use any Alcremie form, it makes no difference.)
Alcremie-Mint-Cream (F) @ Sitrus Berry
Ability: Sweet Veil / Aroma Veil
EVs: 252 HP / 252 Def / 4 SpA
IVs: 0 Atk
- Dazzling Gleam
- Helping Hand
Decorate allows Alcremie to give its ally a free +2 boost to both their attack and special attack, which is absolutely insane. Not to mention you can spam it on your ally and get them all the way to +6 attack and special attack. Also, Decorate ignores protect, so Alcremie can give its ally the boosts without fear of them getting knocked out before the turn ends. Protect gives Alcremie a turn of safety, which is really nice since an opponent might try to take out Alcremie as quick as possible to stop it from making its ally incredibly strong. Dazzling Gleam is STAB and causes spread damage. Helping Hand makes your ally's next attack even more powerful. Sitrus Berry gives Alcremie instant recovery which, in doubles, is better than the passive recovery provided by Leftovers due to the much faster pace. Either of Alcremie's abilities can work for this set. Sweet Veil keeps Alcremie and it's ally safe from Chlorophyll Venusaur's Sleep Powder (and the rare Hypnosis from Politoed and Ninetales but don't worry about those), while Aroma Veil prevents Taunt users from shutting down Alcremie's Decorate shenanigans.
Short replay showing the power of Decorate Alcremie:
Decorate boosted Victini in sun. Yes I know this is kinda low ladder and I didn't show Sweet Veil. I was on my testing alt. Oh and I finally got a better replay after not using it for a month.