Something that I would like to talk about are the brought up similarities between Darkrai and Iron Valiant, and I'll be real with ya, IV is better.
First off, lets see what Darkrai brings to the table.
Darkrai for attacking options has:
Dark Pulse (only stab option)
Focus Miss
Hex (couldn't be too bad on a T-wave or WoW set)
Ice Beam (nice in a tusk meta)
Psychic and Psyshock (not too good due to kingambit and plenty of psychic resists existing)
Shadow Ball (you already have stab dark pulse)
Sludge Bomb (legit nice against fairies, very important)
and... Thunder? Which could be nice in rain ig
Yeah as it turns out darkrai has two 70% acc moves that it would want to run to have required coverage, which isn't the greatest.
It also comes pre-packaged with plenty of support options, including hypnosis for cheese, and both CM and NP
So pretty good, all things considered, and it comes off of a very good 135 SpA and very fast 125 speed. Overall it can absolutely clean up games, and can pick and choose it's counters decently well.
However, one thing that I could like to point out is it's typing and bulk. This thing dies to a small rock, and is the epitome of a glass cannon. Even if you run HDB to increase your longevity, this thing without set up will almost never kill from full, and gets absolutely rocked by U-turn. You hit this thing when it switches in and it's suddenly on life-support. It's 70/90/90 bulk is "decent" and lets it survive at maximum 2 hits. One wrong match-up and this thing is either getting forced out or OHKO'd from full.
So, in summary, it's a fast, frail wallbreaker that can clean up games, while at the expense of needing help switching in and generally being weak to priority. It'll be something that will definitely cause meta adaptations if dropped from Ubers, and looks really solid on paper, with some notable weaknesses.
Meanwhile, Iron Valiant has:
Aura Sphere (stab), Close Combat (stab), Energy Ball, Fire Punch, Future Sight, Grass Knot, Hex, Hyper Voice, Ice Punch, Knock Off, Leaf Blade, Liquidation, Moonblast (stab), Poison Jab, Psychic, Psycho Cut, Psyshock, Shadow Ball, Shadow Claw, Spirit Break (stab), Stored Power (?), Thunderbolt, Thunder Punch, X-Scissor, and Zen Headbutt.
I didn't space the moves out so it might look small, but thats 25 potentially viable stab and coverage options that Iron Valiant could run, with a generous mix of physical and special attacks. Additionally, Iron Valiant gets hypnosis, also gets CM, along with SD, and also gets T-Wave. It's got 130 attack, and 120 special attack, and also gets encore and all of the support moves Darkrai gets, excluding WoW.
"But Elec-ant!" I might hear you saying. "what about it's bulk?", to which I answer... 74/90/64.
In a world where pretty much every priority move is physical, this means that Iron Valiant is literally bulkier than Darkrai, and straight up has a better typing. It has better and more powerful stab options (stab on two amazing attacking types might I add), and almost identical support options.
Iron Valiant, is a fast, frail wallbreaker than can pick and chose it's counters, has amazing coverage, and guess what? Iron Valiant doesn't actually need help switching it. It has actual resistances that are meta relevant, and after it does switch in, oh no! Iron Valiant just encored my resisted hit, SD'd up, and won the game! It literally has an easier time setting up for a win than Darkrai does, since Darkrai has 4MSS, would be absolutely reliant on substitute, would lose to U-Turn, a widely distributed move that's very easily splashable on plenty of OU viable mons, and only can use special moves.
Iron Valiant gets the ability to force your opponent into 50/50's on whether or not to send in a physical wall or special wall. Darkrai will have to rely on Focus Miss, hypnosis, and it's moveset of 9 viable moves to get past anything mildly bulky. Not to mention that Darkrai's ability to benefit from tera will only matter if it's getting KO's. it can't use it's tera defensively due to being a wet sponge with a glock, and if you use it offensively you'd better be running LO and taking 25% from spikes.
TLDR, I believe that even with Darkrai's flutter mane level SpA and good coverage spread and access to tera, it's not gonna be too different from Iron Valiant, who in most cases is just better than Darkrai. Darkrai will be super strong, don't get me wrong it can absolutely clean up games and be a beast, but overall will most likely be very unreliable, wheras Iron Valiant is a meta tested mon who consistently hits top 30% usage, and is one of the most consistent game ender's out there.