And I present the you the worst incarnation of Leafeon that has ever been presented: Special Leafeon.
Leafeon @ Weakness Policy
EVs: 252 SpA, 200 Spe, 56 SpD
Nature: Modest (+SpA, -Atk)
Simple. When you can, set up with Work Up to raise Special Attack. Follow it up with Sunny Day + Solar Beam combo. If Weakness Policy activates, taking in all its boosts (Modest, 252 SpA EVs, Work Up, Weakness Policy, STAB, 120 BP) and getting a super-effective hit will be deadly. If only Leafeon had a better Special Attack stat.
Kind of simple again. Make your Leafeon female for this. Use Attract against male opponents to stall them and get a good Sunny Day + Solar Beam combo off. Synchronoise is kind of questionable, but deals with the occasional Grass/Poison types like Venusaur and Victreebel. Plus, it might come in handy vs Virizion or Chesnaught.
This strategy has a clear focus all around and has some synergy. The traditional Sunny Day + Solar Beam combo goes first this time. Recover health with Synthesis and cover stuff like Gengar with Shadow Ball. Not much to say.
Nevertheless, this strategy is still terrible and you shouldn't consider it for competitive. Dear God just use Physical Leafeon or Wall Leafeon.