Offensive Cloyster?
Hi trainers.
Im seriously thinkng about to power up this Cloyster (hp/atk/def = 15/13/12). I have a Lapras with Ice Shard/Blizzard, but i dont feel nice dodging with Ice Shard. Someone did it? he got a massive defense buff, but HP still very low...so what about huge defense X low hp?.
P.S.: i know, no candies enough to max but he will be my next buddy if worth it.

Answers
I'm in the same boat with my only Shellder...Problem is Cloyster and Dewgong seem better for prestiging so keeping their CP low seems like a better idea...It just has too few hitpoints to take out a lot of Dragonites assuming you have a stronger ice moves attacker (Lapras) so powering it up to Lvl 30 will still only get you 84 hitpoints (sorta like Jolteon, but weaker on attack and HPs).
It looks like we are in the same boat, Focke. I have two Cloysters that I consider powering up. One is 96% IV and lvl 20 like yours, the other one is lvl 27 and boasts good IVs in attack/stamina while having low defense IV.
As Cloyster is already a defensive monster due to his insane defense base stats, I have considered the possibility that he might be worth powering up to help my Lapras take down those pesky Dragonites that pile up in my neighbourhood gyms.
I will give the latter one a test this afternoon and see if he holds up as well as I think he might do. It would be great to see some calculations that documents whether or not his pristine defensive stats makes up for his low HP.
I am pretty sure he is using the hydropump Cloyster as a buddy because it's more convenient. As far as I know, hydropump would only be an optimal move as a defenders move against attacking Arcanines/Flareons.
His low HP makes Cloyster a suboptimal defender in any case. In the updated Gym Defenders List, he's only at tier 3.