Alakazam for offensive core:
+Spd/-Atk or +SpA/-Atk
252 Spd, 252 SpA, 4 Spc Def
Trait: Magic Guard
Item: Life Orb
Psychic
Shadow Ball
Focus Blast
Wild Card move (Encore, Disable, Charge Beam, Energy Ball, Calm Mind, Psyshock, taunt)
Definitely an offensive finisher. This thing has amazing power and speed on it's own. Then give it the ability to use life orb without repercussion and this thing is lethal. It's ability also allows it to ignore damage from weather, hazards, burn, and poison so you can switch this into any hazard and nearly any wall that's trying to set up- which is perfect for bringing in late game and sweeping the house.
It's first three moves give it all sorts of coverage and the 4th move is really up to personal preference. Encore and Disable both work to wreck someone trying to set up. Encore is pro for movelocking pokemon in non-damaging moves so that they either have to switch out or flat out eat a loss. Disable is great for shutting down scarves, bands, etc, and pokemon that set up and/or generally only use one attack move and the go-to counter for toxicroak's sucker punch. Energy ball is for more type coverage. Charge beam is good for finishing weakened pokemon while boosting your already incredible SpA to help make sure it ohko's whatever they try to match it up with next.
Used less often is the Lum/synchronize alakazam that counters gimping stallers with their own medicine while coming out it just healthy. Probably best paired with Disable so it doesn't simply try again (if you're expecting the foe to actually survive a hit). Sporeloom has nightmares of this Kazam.