Hydro Pump is a solid choice over Scald, if you think you can't miss, otherwise, less power, but still, a 30% burn rate and 100% accuracy, having said that:
Team started with a Tapu Koko+Primarina build, I decided to use a different Tapu Koko set, reason being, Assault vest Tangrowth is everywhere and can wall/scout which move Prima will be locked on without problems, physical Tapu Koko allows me tho comfy 2hko tangrowth with a combinaiton of Nature Madness+Brave Bird, same for other more uncommon, but threatening stuff like Amoonguss and Pdef Mega Venusaur (the latter requires Stealth Rock in order to 100% ohko though) Iapapa berry is used in order to lure the opponent into thinking it's one of the taunt set, which helps me against stall, it also helps me against Specs Ash Ninja somehow, if Scizor can keep rocks off the field (or if Greninja is orb) but more of that later with a replay.
Decided to add MScizor in order to get a steel check, especially a Mega Metagross check, Defog support, and basically excellent type synergy + slow u-turn in order to give Primarina an easier entry since it's actually quite frail and slow, ev spread is nothing too fancy, just speedcreeping Specs/av/chople Magnezone who wants to speedcreep Mega Scizor, and also 80 uninvested base speed like MVenusaur, rest goes to defense in order to tank Megagross, even if it were able to get a Meteor boost. Team by now lacked speed control and serious ways to handle stall, enter Scarf Ninja, the only fast scarfer with U-turn, since I'm planning to use Landorus later on, Greni also helps me with Volcarona without charti, though it has difficulties setting up on its own against this team, especially now that I'm not scared to click Primarina's water stab, with a core of 3 uturners that can help Primarina coming in, I now decided to concentrate the last two slots on having better odds against stall, and, of course, Stealth Rocks. So i added Swords Dance Lantherian with Stealth Rocks, Jolly in order to outspeed other Fast Adamant Landorus who can be dangerous if left on his own devices, after this, the team had troubles against 3 atk Zapdos, and, while I prefer Rock Head Marowak generally, Lighting Rod was the better choice here, in order to have a better matchup against Tapu Koko, 3 atk Zapdos, MManectric when released, it also helps me against stuff like Mega Venusaur who I mentioned earlier, sure Koko can 2hko, but how can it take a Sludge Bomb from it? I must have something to switch into it and scare it off, and since I already had Defog MScizor, why not SD Marowak? Bonemerang could be a better choice since it breaks sub, but honestly it's the same thing with Hydro Pump to me.
All in all, I had fun with the team, however Primarina sometimes wasn't able to do much, maybe it had something to do with me finding bulky offense teams with a random Chansey slapped on it wth but there were some battles that primarina was allowed to shine.