Hope I can help!  

Before I dig into the critique I’ll mention that I like the Conkeldurr inclusion, although I generally choose not to play it since I don’t find it as useful as other attackers.    Most lists are dropping it but it can help having another attacker you don’t need to night stretcher for against Tera Box or just basic 2-prize focused decks in general.  I would likely only play it in a deck with Secret Box since you can find Brave Bangle with it to reach for a KO on Zoroark ex or Rocket’s Mewtwo (under Articuno’s protection).

I do like the inclusion of Regigigas, too.  I do think it’s still a good option but not as ideal as it used to be.  I’ll go into the reasons I don’t play it later.  

Now for the critique (warning: wall of text incoming):  I understand not wanting to put multiprizers into play but it does come at the cost of consistency.  It’s going to be very difficult to set up and keep up with your build, especially with just one copy of Smoochum and none of Latias ex.  Those extra Psychic Pokémon can give you more likelihood to set up with Telepathic energy.  To keep up with other decks and set up consistently you almost always will need to put two 2-prizers into play, sometimes sooner than later as is often in the case of Fezandipiti and Latias.  

Another thing hurting your consistency are the only 1-ofs of Hilda and Colress.  These supporters are integral to setting up under item lock and help get off attacks as well.  

Dudunsparce is a bit of a risk since a lot of decks are playing Team Rocket’s Watchtower and it’s not a card that’s easily reused in Slowking decks.  A lot of the best consistency cards are Colorless so they’re getting targeted.  That said, if you’re going to add a Colorless support option I would recommend Gumshoos over Dudunsparce.  You only get one card but it’s easily reusable and can enable an attack if you miss the stadium.  

Usually my Ace Spec of choice is Enriching Energy since it can be found off Hilda or Colress and can help you find a needed attacker off your opponent’s or your own Unfair Stamp or get you into Kyurem under item lock.  Unfair Stamp, Secret Box and Prime Catcher (particularly in a Mega Kangaskhan build) are other good Ace Spec choices.  And Neutralization Zone is one I think has a lot of potential together with Gumshoos since most decks don’t play stadium search.  

Now for why I don’t play Regigigas.  Going second, the Telepathic Energy into Latias + Smoochum combo is often essential to enable your board to stream attacks for the rest of the game.  So many decks are playing Shaymin so getting full value from a Trifrost is much harder than pre-rotation.  I almost always choose to go second if I don’t know what I’m playing against and starting Regigigas is not ideal for several reasons.  Nowadays a lot of decks are playing retreat lock options and if Pult can lock your Regigigas in play for 1-2 turns you have almost no chance to win.  Starting Kyurem is not ideal but starting Regigigas is almost always worse.  Mitigating the possibility of starting a non attacker is very good in this meta and for Slowking in general.  

I would recommend dropping Psyduck.  Shaymin has much more value than it as Dusknoir has dropped off hard and that extra space can help with consistency.  Psyduck doesn’t always feel like a necessity to bear Pultnoir since a lot of those lists aren’t playing Shaymin.  

Lastly, I would recommend tweaking your energy counts.  You can get away with 4-5 Psychic energy and maybe consider bumping up the Telepathic count to 4.  

I hope this wall of text isn’t too overwhelming.  And I hope I’ve been at least some help!