just got reqs and gonna post some thoughts :
The main thing I feel about Serperior, that is pushing it over the top is Glare, which IMO is a staple move on any non stallbreaking set (Taunt|Synthesis).
Serperior is really crazy in the meta as it IS currently a bulky water dominating meta, with the likes of Suicune and Pert.
With Serperior in the meta, how can running such dominating forces(the bulky waters) can turn into liabilities, can be not broken meta?
The snake user, when faced with a faster "counter" in the team preview (bat, beedrill, aero, etc) and a bulky water at hand, it faces with a crucial choice between Leaf Storming or Glaring. When choosing to Glare, it must be punished! Therefore, if those bulky waters have any means of punishing the snake...
Suicune - Sub 3 attack and SubCM are all getting more popular with threats like Mence(IB) and heliolisk(sub).
Swampert - having such glaring weakness to grass, only focus sash can save it from snake so if snake stays, swampert loses viability. It just dies to any grass attack, there's no discussion about trying to live a hit but ofcourse Ice Beam (or Ice Punch on mega) is a viable option already on top of rocks|eq|scald.
Vaporeon - I tried to fit in Ice Beam but it just wants so many others moves in Scald,Wish,Protect AND Baton Pass which is too good to pass on.
Milotic - I know it's considered bad, but Snake loses 1v1 if it switches in on due to Toxic and Ice Beam.
Empoleon - thought less of bulky water in this department, as it is hit neutrally by grass, but fitting Ice Beam isn't hard. (instead of Roar, or having another rock setter)
In fact, Serp is really hard to switch in. Any good Serp performance I've seen was on either HO or serp was (one of) the win con., and something else had to die in order to let Serp come in safely. That right there is a dangerous meta imo, when you should consider carefully if to KO a mon and with whom for the fear of Serp coming in safely.
I don't think Stall has any problems really, other than having to fit into their already tight slots, a counter for serp but counters to exist! (Roserade/Amoonguss)
Outside of glare, I think if any 'mon could receive +2 move and a contrary and be not broken it's serperior. I mean, other than those, it has all the bad qualities :
- Grass is arguably the worst mon-attacking typing with vast resists in Flying, Fire, Poison, Bug, Dragon, Steel and with just two SE types. (Rock types are almost non-present and Aero is faster and takes neutral damage from grass)
- Snake's coverage options are shit, outside of Dragon Pulse, which is useful against one out of six of it's type resists, it has to resort to Hidden Power.
- low initial SpAtt (yeah, mitigated by high BP of LeafStorm...)
However :
- Glare, unlike other paralyzing moves, has 100% accuracy, which is huge imo.
- the ability to choose HP (fire or ice mostly) mean Serp is much more unpredictable and that can decide matches.
- Although lacking the ability to boost own speed (besides opposing sticky web), it sports such a high and defining speed tier which really a select few naturally outspeed it.
Sorry for the incoherent rumble. I just wanted to post some thought from either side.
I'm currently slightly leaning towards non-ban but I'm really swinging right now.