Ophie
Salingerian Phony
I love her <3
Dragon Darts is the best physical Dragon-type move without any drawbacks. Similar to Bonemerang, it is like an Earthquake that can break Substitutes.
However, targetting each target in double battles may not always be beneficial.
I get the feeling Dragapult requires pretty different moves between single battling and double battling, more so than usual. That being said, a spread move may still be useful even with low power like Dragon Darts. It can use Dragon Darts if both opponents havelow HP to knock them both out at once, but taking into account Dragapult's mad Speed, you are very likely to be in control of when that happens. At a base Speed of 142, I believe Dragapult is the fastest Pokémon with a spread move that doesn't also hit the ally (though anyone can correct me if I'm wrong).
Wishing Star looks familiar...
Eternatus' body part? Speculated to play role in D-G/Maxing.
But isn't Jirachi already a Pokémon themed on a wishing star?
Okay, I'm I'm just gonna say it. If Eiscue has Follow Me, it will kill all Double Battles.
Just imagine it. Leftovers Eiscue uses Follow Me so Choice Band Snow Cloak Mamoswine can activate Hail, then Eiscue constantly redirects attacks while Mamoswine Earthquakes the hell out of everyone. Not an exact thought, but pretty dope in theory. Either way, Follow Me would be an interesting move for Eiscue to have.
A bit of a heads-up: Ice Face apparently only works on physical attacks. Special attacks will still pass right through that big head of Eiscue's. You have to be very careful whom you're up against, and similarly, an opponent can easily counter Eiscue by sending out a special attacker.
That's actually a theme I'm seeing with the stats of the Generation VIII Pokémon. If it isn't a glass cannon, then it likely has a very high stat on one side but below-average to low on the other. I'm seeing this with Perrserker, Galarian Stunfisk, Sandaconda, Falinks, and Duraludon on the physical side (high Defense, low Sp. Defense) and Alcremie, Cursola, Cramorant, and Frosmoth on the special side (low Defense, high Sp. Defense). Switching will be even more important than ever, even in double battles.