Cloyster - OU because it is so common and can beat the 2 other Spikers like Skarmory and and Forretress and spin away their Spikes and can 2KO them with Ice Beam/Surf. It also isn't trapped by Magneton and if it uses Clamp on either Skarmory or Forretress and has Rapid Spin in it's arsenal, Spikes are yours for the rest of the match. It also has STAB on Ice Beam, which IMO, is pretty useful for the ever dominant Dragon types like Salamence and Flygon.
Steelix - BL because since when was this metal snake used a lot, apart from GSC? And that base 200 defense is hampered by weaknesses to the ever common Earthquake, and some physical attackers can beat Steelix one on one such as Breloom, Marowak and bulky Fighting types like Hariyama, Machamp and Hitmontop. Skarmory is better if you want a physical wall, and Skarmory can actually Spike up the field while Steelix's support is limited to Toxic.
Exeggutor - BL because hardly anyone uses him in RSE, and if the every popular Tyranitar switches in the moment he Solarbeams, he is screwed. Although I do admit that with Sleep Powder, Stun Spore and Explosion nothing is completely safe from him.
Swalot - UU because he is supposed to be there. What makes people think Muk is better than him? Swalot has his own fair share of tricks, including Encore and Pain Split. He can also use Special Attacks like Ice Beam and can also go physical with Explosion and Shadow Ball.
Piloswine - UU because Ground + Ice is unresisted in 3rd generation, and with base 100 attack Earthquake from this thing will do some damage. And it can also take hits relatively well with base 100 HP, although it's typing is extremely poor defensively.