Ambipom: too frail to be worth it. maybe an OK BPer, but there's better for sure.
Mismagius: tankier Missy is always a plus. after Protect it fails to be 2HKOed by Tyranitar Crunch. BKC already mentioned the benefits of the Speed; Nido and Zapdos are two key advantages there. Stronger Thunder that guarantees a 3HKO on Suicune (provided they all hit of course) is also a plus. Same set as Misdreavus currently has.
Honchkrow: Unfortunately its bulk blows. That said, it's a Pursuiter with decent Special Attack that Egg can't touch and Starmie fails to 2HKO, albeit at the cost of being scared shitless of Gengar and Misdreavus Thunders. Probably not worth it. Drill Peck/Pursuit/Thief/HP Dark might be the set?
Weavile: Enough SpA to 3HKO Zapdos with Ice Beam now. That's a plus. Still mostly ass though.
Magnezone: Magneton that actually avoids being 3HKO by most Surfs and has a Thunder that's stronger than Zapdos'. This looks like fun. Especially for passing Growths against a team that uses MonoLax. It doesn't really bend the meta to its will or anything like that, but it's a decent mon with a decent niche that fits well in the existing meta. Same sets as Magneton currently has, probably a little more likely to run Sleep Talk than SubWave, though.
Lickilicky: Swords Dance Lickilicky is dangerous as shit. If you thought Tenta was bad, wait til you see this beast that can stay in on basically anything. Actually gets STAB too, unlike Mew in Ubers, although it just misses out on the all-important base 55 speed tier. Frustration/Earthquake/Fire Blast/Swords Dance is the set. Maybe Bslam or DE as the STAB, idk.
Rhyperior: Basically a better Rhydon. Rhydon's already good. The extra stats mean Rhyperior has a chance to 3HKO Lax unboosted and fails to get 3HKO by Lax's EQ in return. Not being 2HKOed by Gengar Ice Punch, guaranteeing that Zapdos HP Water doesn't OHKO, and having an EQ that can actually OHKO Raikou are also nice bonuses. As are a Rock Slide that can 3HKO Heracross and a Flamethrower that 3HKOs Skarmory (to avoid Fblast PP woes) or a Fire Blast that has a realistic chance to OHKO Forretress. Probably more likely to run coverage than standard Rhydon right now; you could see something like EQ/RS/ZapCannon/Curse, or if a team needs a Phazer for Mismag/Umb, EQ/RS/FB/Roar. SubCurse is also a more realistic option with Rhyperior.
Tangrowth: Special Bulk blows, so it can't tank Electrics like Meganium can. It also misses out on Leech Seed, so that nice Physical bulk can't really be used effectively. Tangrowth stinks.
Electivire: Misses out on Buzz's good Speed tier (outspeeds Zapper and Miltank), but that's merely inconvenient. It more than makes up for it with a mighty Attack stat. After a meditate, it 3HKOs Raikou with CC and 2HKOs Snorlax. There's also a realistic chance to OHKO Steelix with a +1 CC crit after Spikes damage. This is a dangerous mixed attacker that GSC isn't really well-equipped to handle. Thunder/IP/CC/Meditate.
Magmortar: It's kinda like a Moltres with better coverage and the ability to survive two Zapdos Thunders (let alone one). Unfortunately, it still doesn't deal with bulky waters too well (Tpunch won't 3HKO), its Speed tier is unfortunate (outsped by Nidoking and Suicune), and its Physical bulk is pitiful (still 2HKOed by Snorlax DE most of the time). There is something to be said for Cross Chop on something with a face-melting SunnyBlast, though; Tyranitar utterly fails to check it, which is how a lot of teams actually handle Moltres. Bulky waters aren't absolutely everywhere, ya know... Fblast/Sub/CC/SunnyDay.
Togekiss: Ew. No Attack stat to speak of, no Special STABs, no Serene Grace... most it has is Charm, which just isn't enough.
Yanmega: LOL this thing is garbage.
Leafeon: Pretty similar to Tangrowth, actually. Only it doesn't even get Swords Dance. Better Defense stat than Umb is nice, but its HP means its Physical bulk is still worse. I guess it has a tiny niche in being able to Charm Machamp, do enough damage with Frustration to deter DrumLax (Frustration does damage on par with Miltank Body Slam), and if it's like the other Stoned Eeveelutions, actually having Roar to deal with CurseDrum variants and Vaporeon. Frustration/Charm/Roar/Synthesis would probably be the set.
Glaceon: Everyone seems to be creaming themselves over Glaceon. I think it's good but pretty limited. Better Physical bulk than Vap for tanking Laxen a little better, but no AA to let it set up in its face. Isn't countered by Electrics but still can't really switch into them. Beats Egg but has a little trouble switchin in. Loses to Vap. Puts very little pressure on Cloy to Explode, unlike Vap (unless it runs coverage, but no ST is pretty lame in terms of survivability and availability). Can't set up on Ttar/Steelix. Overall probably OU, but between Vap and Espeon in terms of usefulness imo. IB/Growth/Rest/ST
Gliscor: Gligar's main issue has always been its movepool. Gliscor's better stats therefore don't mean a whole lot. That said, its EQ is actually respectable and it's no longer OHKOed by Hidden Power Ices, so it can actually threaten to Counter them back. EQ/Screech/Counter/Rest is probably the set. Maybe Toxic or Thief over Screech or Rest, idk.
Mamoswine: Rhydon-like Attack, a Speed tier that puts it above Vap and Exeggutor, the same Zapdos-tanking action we love about Pilo, and an Ice Beam that can (rarely) 2HKO Zapdos and does respectable damage to Skarm. Yep, this thing's a beast. EQ/IB/Curse/Rest (Curse is nice because it outpaces Lax at +1!!!!)
Porygon-Z: Definitely something to be said for a mixed attacker with Physical STAB stronger than Nidoking EQ, base 90 Speed, enough SpA to 3HKO Cune with Tbolt, and instant recovery. DE/IB/Tbolt/Recover. Setting up with Curse probably isn't super great because STAB Thunders from legends are likely to 2HKO (although that Speed means outpacing Lax at +1 and getting an extra hit off on Umb). Maybe Sharpen is a thing to outspeed Suicunes at +1?