This is the best Lampent set, imo, and probably the only Lampent set I'd use.
[SET]
name: SubSplit
move 1: Substitute
move 2: Pain Split
move 3: Fire Blast
move 4: Shadow Ball
item: Eviolite
ability: Flash Fire
nature: Modest
evs: 212 HP / 252 SpA / 44 Spe
[SET COMMENTS]
<p>There are a lot of top threats that Lampent can easily take advantage of. For instance, Lampent can easily set up Substitute on Amoonguss, Gurdurr, and mixed Emboar. Defensively, a Fire / Ghost typing has plenty of useful resistances and immunities, such as resistances to Grass-, Fire-, and Ice-type attacks and immunities to Normal- and Fighting-type attacks. Offensively, the typing provides virtually unresisted STAB coverage in NU save for Thick Fat Miltank. It's not that hard for Lampent to set up a Substitute. After Lampent uses Substitute, it can hit the opposing Pokemon hard with either Fire Blast or Shadow Ball, or recover health with Pain Split. Despite its base 95 Special Attack, STAB Fire Blast will still do a lot of damage.</p>
[ADDITIONAL COMMENTS]
<p>44 Speed EVs allows Lampent to outspeed uninvested base 60 Speed Pokemon such as Tangela. 252 Speed EVs can be used to make Lampent as fast as possible and maximize the health regained from Pain Split. However, Lampent is still not that fast even with Speed investment, and it appreciates the extra bulk. Lampent is quite powerful with Life Orb, but then Lampent loses a ton of bulk that it really needs. Calm Mind is an interesting option over Substitute or Pain Split, but both moves are very important and Lampent is not the optimal choice for a sweeper thanks to its mediocre Speed.</p>
<p>Lampent can beat a lot of Serperior's checks, such as Amoonguss and Charizard, while Serperior reciprocates by beating Water- and Rock-types, most notably Regirock. Omanyte synergizes pretty well with Serperior and Lampent and can set up Spikes and Stealth Rock which both Pokemon are adept at abusing. Armaldo is a decent teammate for Lampent, as it can spin away Stealth Rock, but it doesn't synergize well with Lampent as both are weak to Water- and Rock-type moves. Piloswine beats some Pokemon that Lampent can't get past, such as Altaria, and can also set up Stealth Rock. In addition, Lampent is immune to the Fighting-type attacks that Piloswine is weak to.</p>