Here's a few thoughts:
Stunfisk is great, spdef fisk with SR / EP / Discharge / protect or toxic walls stuff like Electabuzz and Electrode while also being one of the more reliable SR users in the tier. I've decided to pair it up with Metang on offensive teams as Metang can check Articuno and Simisage (kinda) which both beat Stunfisk pretty easily. It fits on most balance/semistall/stall teams pretty easily and can even serve as a pivot on offensive teams for Electabuzz/Electrode since offense generally suffers vs those two and could use another viable SR user.
Rampardos is a great wallbreaker with a lot of different sets, including 4 attacks, 3 attacks RP, or sashlead with SR. It is really slow and has a hard time not being revenge killed by pokemon like Krokorok, Gabite or Simisage so it should be fine in the tier, but with the addition of Rampardos, balance and stall has a hard time pulling off any sort of good defensive cores because Rampardos specializes in ripping them apart along with other breakers like Flareon.
I'll have to do more research into meowstic, I never really used it when it was here and I guess the one obvious niche is prankster screens for offensive teams with setup pokemon, luckily we lost Arbok because Meowstic-M with 8 turn screens + Coil Arbok sounds really devastating, lol. There is still plenty of options for setup pokemon like DD fraxure, Agility Kingler, etc so it's got a lot of potential.
I really like losing Arbok, since I personally believed that Arbok was one of the most broken pokemon in the current metagame having the ability to easily setup on defensive teams (especially with SubCoil) and then break through offensive teams with defensive boosts, Sucker Punch and STAB Gunk Shot. Duosion was cool but I never got the chance to use it, it seemed like a nice CM user or even offensive TR user which could be fun to use but I can't really speak on its effectiveness since I never got the chance to use it.
Losing Simipour was bound to happen eventually based on how good it is in PU right now but it's a drastic change for FU. Simipour was the best offensive Water-type we had and was a huge asset to offensive, being able to break through defensive cores easily especially with Taunt and being damn fast to outspeed most of opposing offensive teams, with great coverage with Hydro Pump, Ice Beam, HP Electric/Grass and Knock Off, not to mention Sub + NP + Salac which is a really cool set too. Losing Simipour means offense loses a fast Water-type and the only other fast offensive water type we have is Swanna, because Golduck needs rain to have speed and doesn't serve the same purpose that Simipour does, not to mention with the same effectiveness. Really sad loss but was inevitable, I guess we'll have to see if Golduck/Politoed/Swanna/Lapras usage goes up as it should in the coming months.