The analysis currently has Leafeon's counters in OU, but none of its UU counters, rather relevant since it's been moved to the UU tier.
http://www.smogon.com/dp/pokemon/leafeon
[Counters]
<p> Drapion can come in easily on any of his attacks and hit him with STAB Poison attacks and can also Whirlwind away any Swords Dance boosts. Muk can work in a similar manner using Haze. </p>
<p> Altaria can also Haze away Swords Dance boosts and 4x resists Leaf Blade. Steelix and Aggron can Roar Leafeon away, but repeated hits from Leaf Blade will take their toll. </p>
<p> Most Fire and Flying-types can stop Leafeon with relative ease, but Leafeon will often just Baton Pass to another Pokemon, though faster Pokemon and Will-o-Wisp can often negate this strategy. In general it's better to target Leafeon with special attacks, as his Special Defense is much lower than his Defense </p>
http://www.smogon.com/dp/pokemon/leafeon
[Counters]
<p> Drapion can come in easily on any of his attacks and hit him with STAB Poison attacks and can also Whirlwind away any Swords Dance boosts. Muk can work in a similar manner using Haze. </p>
<p> Altaria can also Haze away Swords Dance boosts and 4x resists Leaf Blade. Steelix and Aggron can Roar Leafeon away, but repeated hits from Leaf Blade will take their toll. </p>
<p> Most Fire and Flying-types can stop Leafeon with relative ease, but Leafeon will often just Baton Pass to another Pokemon, though faster Pokemon and Will-o-Wisp can often negate this strategy. In general it's better to target Leafeon with special attacks, as his Special Defense is much lower than his Defense </p>