Is Cloyster the only 4-Tier Raid solo able?

Cloyster is tier 2, yes it is soloable

It is by far the most difficult 2 tier raid. I have more trouble with it than some of the tier 3.

Cloyster is not easy but doable solo with the appropriate lineup.

I used 3 Machamps (lvl 35 C/DP, lvl 32 C/KC and lvl 31 C/DP) and 3 T-tars with B/SE (lvl 38.5, lvl 32 and lvl 32).

Cloyster had Avalanche and I beat him with 11 seconds left.

It should be one of the hardest if it were a tier 4. No, even Woopers are not soloable as a tier 4.

OK, good to hear others had trouble with it. I lost to it the first time when I used a less than ideal lineup against it. Did beat it with two powered up C/DP machamps, a powered up raikou, and a powered up C/SE ttar, with about 20 seconds to spare.

It is tier 2, the hardest one so far, more fit to tier 3 imho
But yes still soloable...

Cloyster was surprisingly difficult for a T2 - I beat on the first try, but with only 15 seconds left. It had a mixed moveset - IS/HP.

I used two Machamps to start and a bunch of grass types with SoB to finish him off (all 30+).

Yes, if they made Porygon a tier 2 and Cloyster a tier 3, with no other changes at all, it would make sense. Likely that making Cloyster a tier 3 will make it even tougher, though.

I like how he is a Tier 2 Boss. Catched many trainers by surprise for sure.

Still have to find one. I saw quite a few around the first days. But I didn't care. Past week I was looking for him but nope...He is ducking me somehow