Always thought Mesprit was kind of cool:
Mesprit @ Leftovers
Trait: Levitate
EVs: 92 HP / 252 SAtk / 164 Spd
Timid Nature (+Spd, -Atk)
- Stealth Rock
- Psychic / Psyshock
- Thunderbolt / Ice Beam
- U-turn / Healing Wish
So, by all the slashes, you can get the idea that this is a fairly flexible set. The idea is to let Mesprit act as a bulky pivot on Offense teams with its solid bulk and offensive presence. SR is SR. It's the best entry hazard move in the game and Mesprit can find many chances to set it up. Next up is Mesprit's STAB move. Psychic deals more consistent damage, but Psyshock is a viable alternative to better handle Gallade, a Pokemon Mesprit can check quite nicely, especially in the absence of Night Slash. Next move is Mesprit's coverage option. As Mesprit draws in many Steel-types, Thunderbolt is preferred to hit the majority of them for at least neutral damage. It also catches Slowking for super effective damage and Mesprit can check it nicely. However, if coverage on Steelix, Druddigon, and Grass-types in general is needed, then Mesprit can opt to run Ice Beam. Do note, however, that Mesprit now gets walled by Slowking and is unable to fend off most Steel-types very effectively when it runs Ice Beam. Finally, Mesprit's primary utility move. U-turn is preferred as it lets the pixie scout for checks and counters. This also allows Mesprit to perform very well on VoltTurn teams as a bulky pivot that still maintains solid offensive momentum. Healing Wish is a riskier, yet more rewarding utility move if played right. If pulled off right, Mesprit can bring back a sweeper to end the match or it can bring back a wall to save the match. However, with Healing Wish, Mesprit is unable to pivot as effectively throughout the early and mid-stages of a match.
The EVs focus on offense, but don't neglect Mesprit's solid 80 / 105 / 105 bulk. Max Special Attack EVs let Mesprit hit as hard as possible while 164 Speed EVs and a Timid nature is required to let Mesprit outspeed neutral base 80 Speed Pokemon such as Gallade and Kabutops, 2 threats that Mesprit can neutralize with Psyshock and Thunderbolt respectively. The remaining EVs are placed in Mesprit's HP to improve its overall bulk. Leftovers is really the only item choice for such a set as it lets Mesprit to better take advantage of its resistances and immunity to Fighting-, Psychic-, and Ground-type moves. That said, a more offensive spread of 4 Def / 252 SAtk / 252 Spe can be used with a Life Orb to eshew bulk in favor of offensive presence. If you go this route, using another coverage move or Healing Wish over U-turn is advised as the LO recoil will make U-turn more of a detriment.
Teammates that can handle the threats Mesprit doesn't cover with its coverage option are very much appreciated. In the absence of Ice Beam, Mesprit is helplessly walled by Steelix while Rhydon will wall Mesprit if it runs Psyshock + Thunderbolt. This means that most Water-types would work nicely. Samurott and Omastar hit from the special side and can benefit greatly from Mesprit's ability to check Slowking (this can also free Samurott to run SuperPower to help Mesprit with Steel-types if you so wish) Without Thunderbolt, Mesprit has no chance against Slowking and will struggle more with Omastar and Kabutops than it normally would. In this case, Grass- and Electric-types are worthy options. Of particular note is Manectric as it loves to have Mesprit weaken Druddigon, its best offensive counter and the two form a little VoltTurn core. Sceptile, Rotom(-C), and Lilligant are also all worthy options to look into.
No matter what coverage option Mesprit uses, an answer to Steel- and Dark-types is a necessity as they will give Mesprit issues regardless of whether or not it runs Thunderbolt or Ice Beam. Emboar, Entei, and Gallade are all useful in this regard as all 3 can handle most Steel- and Dark-types effectively. Emboar in particular shares very good synergy with Mesprit as both resist at least 2 of the other's weaknesses.