Toxapex is one of the most popular right now due to it's decent typing, having a Protect that poisons, Recover, Regenerator. It can be very hard to deal with sometimes.
Araquanid is looking very strong, both as a bulky mon and as a general physical attacker. Which, if any, ends up being dominant remains to be seen, I like to play it as a mixture of the two. Great typing, great moves, great stats.
Mimikyu with Z-Splash and Shadow Sneak is really nice, even with disguise off it seems to have decent bulk. Also has Leech Life which is nice.
Minior in the right conditions can sweep teams very easily, so can also work in certain comps. Dies pretty badly to priority, but if supported by a Tapu Lele I can see it being really good.
UB Pheromosa is pretty decent - not as OP as it might seem, but it's almost guaranteed to get a Lunge off due to its high speed so it's like having an Intimidate off the bat which also does respectable STAB damage, which offsets the squishiness somewhat. If people stop maxing speed, and instead put those points into defense/HP, I think it could turn out very well.
UB Kartana is surprisingly decent, you wouldn't think Steel/Grass is that good offensively but it often means that it can usually take a hit before dying, and then just mince you.
The "not quite as strong as you would expect" tier:
Lycanroc Sun
Bewear
Xirkitree
I also feel Lunge is very underrated as a move and could start getting complaints if it gets abused alot.
