This is my first time making a post like this (hence the flying galvantula) but I thought why not. I've been wanting to try and make a team of my own and this challenge seemed fun so yeah :D
Eternatus isn't a pokemon I know very well or use, but I think I made a pretty fun team here. To introduce this team, Oranguru here knows Instruct. And can have the ability Telepathy which prevents itself from being damaged by adjacent moves like Earthquake, or Sludge Wave. Sludge Wave can be learnt by Eternatus, so if Oranguru does Instruct on Eternatus, it will do Sludge Wave twice. Inflicting double damage on opponents and even having a chance to poison them. And with Life Orb, the damage Eternatus deals will be greater.
(Btw, Dynamax Cannon doesn't work with Instruct. Please be wary of that ehe)
Oh, and Ally Switch is a god send. Just imagine the opponent tries to kill Eternatus with Earth Power, but nope, it's on Oranguru instead. Mindgames are great.
Of course, this isn't easy to pull off. For one, Life Orb will trigger twice if the combo happens. which will cause Eternatus to lose at least 20% HP, which is more than wanted. And two, there's pokemon with Taunt (I am Looking at you Whimsicott) who might Taunt Oranguru and prevent them from using Instruct. And they don't have attack moves either. Mental Herb is on Oranguru to at least cancel the Taunt and give Eternatus or any of the teammates to kill the Taunter. But it's still tricky to pull off.
Just for more coverage, Eternatus has Dynamax Cannon as usual and Flamethrower for the pesky steel types. More importantly, against Zacian. But wait, Zacian might be faster. It might kill Eternatus first. So I will introduce to you the supporting cast.
Tornadus and Galvantula are here to control the speed. You might ask why I didn't choose Regieleki instead, and it's solely because of Sticky Web. Which lowers the speed of grounded pokemon that enter the field by a stage. Icy Wind and Electroweb won't help me forever because they might just switch out. And Tailwind isn't permanent either. So at least Sticky Web can slow them down a bit, unless they have Rapid Spin, for whatever reason.
Still, Tornadus is a great supporter with it's Prankster ability. Tailwind and Icy Wind are there for speed, while Hurricane and Sludge Bomb are just in case he has to go into attack mode for at least a bit of chip damage. Bug Buzz and Thunder on Galvantula is also great. Especially when facing against a Kyogre team. Also don't ask why Wide Lens is on Galvantula. It's personal preference and experience (haha, screw those Thunders.)
Alolan Ninetails can control the weather with Hail, has access to Aurora Veil with Light Clay, and can destroy opponent's pokemon with Moonblast or Blizzard. Icy Wind is also there to, you guessed it, speed control. Can't bring Galvantula and Tornadus all the time yk.
Yes, Rillaboom with Terrain Extender. Solely because I need that healing on Eternatus. I swear the amount of times Eternatus died because of Life Orb made me insane. But that's not the only benefit, as you can tell by Grassy Glide. Oh and Earthquake, well, you can imagine it with Oranguru :]
And yeah, that's basically it. This team definitely has its weaknesses, even with the best efforts to cover it. But when the ball gets rolling, it'll definitely pay off. After playing a lot, I mean a lot, of games with it, it's very fun. Hopefully this team is a tad bit interesting to you maybe >:Db