Blissey @ Leftovers
Trait: Natural Cure
EVs: 136Def / 36 SAtk / 252SDef / 84 Spd
Calm Nature (+SDef, -Atk)
- Gravity
- Sing
- Fire Blast
- Softboiled
So there we were, trying to make the Pink Blos less of setup fodder than it usually is. Point is, we were trying to nail as many switch-ins as possible; it is common knowledgee that practically everyone hates induces sleep, we decided on a Gravity set in order to utilize Sing. With Gravity on the field, its accuracy ascend into a new level of reliability of 92%. As the second move we have chosen FireBlast, to deal with a good chunk of steel types who are prone of their toxic immunity. As a bonus, Fire Blast is actually perfectly accurate under Gravitiy's effect.
Fire Blast itself has a good chance to OHKO CB-Scizor (safe after SR), maybe 2HKO standard Ferrothorn (sure 2HKO after SR), 2HKO physical Skarmory and surefire on physically defensive Forretress. With the additional SAtk Blissey will always obliberate CB-Scizor and 2HKO Ferrothorn without entry hazards. Note, that if you are afraid of Ferrothorn going for the Leech Seeds in the first turn, you always can skip Gravity and lure it into FireBlast. Or, you have a Grass type like Breelom or Virizion in your team, so that the opponent is not too likely to fire of Leech Seed carelessly.
This Blissey should at least be fast enough to outrun CB-Scizor. As you know, more speed is always welcome, so don't be afraid to experiment with the spreads.
EVs: 96 Def / 36 SAtk / 252 SDef / 124 Spd
Calm Nature (+SDef, -Atk)
This one outruns Skarmories without speed investments. The Smogon sets' speed investments are relatively loose, so I won't turn in the speed creep; do it yourself.
You, of course, can leave Skarmory to another teammate, because Skarmory is extremely susceptible to strong Earthquakes while Gravity is under effect.
EVs: 36 SAtk / 220 SDef / 252 Spd
Timid Nature (+Spd, -Atk)
This one ties with adamant offensive Scizor. But really: Offensive Scizors are most likely trying to setup on you anyway, so anything more than being faster than CB-Scizor and maybe Skarmory is speed-overkill.
Everything that can't be disintegrate by Fire Blast and doesn't try to kill you right of the bat is the target of Sing. Reuniclus appreciates Toxic, doesn't mind paralysis too much and may carry Psyshock, so they are likely to come in. Mixed Tyranitars are slower than Blissey, too, and may try to Pursuit-trap it. The DD variant may be faster, but will probably try to setup like offensive Scizor, just to be put into sleep without even having struggeled in sleep for a round as usual it is the case. Conkeldurr is on the same boat, Ferrothorn, too, if you want to play safe instead of risking to take Leech Seed in your face.
A Fire Gem is an option, too. On the sets I've shown the only thing this can accomplish is a OHKO of specially defensive Forretress. When using a Fire Gem, I personally try to at least OHKO Ferrothorn. 240 SAtk will do it, 184 when having SR on the field, 120 when having one layer of Spikes.