Came across a Bulky Attacker Dewgong set the other day in DPP Randbats with the move set
Rain Dance/Surf/Rest/(Encore/Toxic)
I believe this set limits Dewgong’s versatility by giving it only one attacking move and having two moves that are imo functionally very similar, with a few differences.
Rain Dance i) Boosts Water-type moves by 50% ii) Weakens Fire-type moves by 50% iii) Activates Dewgong’s Hydration ability.
Under very niche circumstances you could roll a swift swim user (or have something be changed to swift swim) that could benefit from this, but with limited turns it becomes unlikely and unreliable, and your opponent could roll one too.
The boost to water type moves can be useful when the opponent has no water resist, but dewgong becomes dead weight when they do, being unable to deal much meaningful damage. The weakened fire moves is can be helpful, but most fire types won’t want to come in on dewgong and quite a few carry super effective coverage moves for it (eg TFang Arcanine or Superpower Flareon)
Healing statuses on Dewgong is relatively negligible because Dewgong is guaranteed to also pull rest, which removes status and heals to full at the downside of making you unable to move for 2 turns following. Keeping in mind Rain Dance takes an extra turn to set up, Rest heals to full and heals status in exchange for essentially 1 turn immobile, while rain dance only heals status. RD can be better in certain niche situations where the other effects are useful but overall this is unlikely and limits what Dewgong can do in a game.
Having a roll for encore or toxic is quite annoying too because encore generally isn’t going to get much use when Dewgong can’t do much in return for except setup rain dance.
Having Toxic is much more useful but it is only useful because Dewgong can’t do more damage by attacking with pitiful attacking stats and limited attacking moves as mentioned. At the least, Toxic should be guaranteed so Dewgong isn’t incredibly easily walled by any water resist and might be able to stall certain pokemon but even this is unlikely imo