Lugia, the sea guardian Pokemon!(who is not a water type for some reason).
Lugia has immense bulk and the infamous ability multiscale.
It serves as a potent blanket check and emergency switchin to some of AG's most potent threats, including Mega Rayquaza, Zacian-C, and Ultra Necrozma. Access to valuable support moves such as Whirlwind and Toxic and Thunder Wave allows it to accrue chip damage or cripple the aforementioned threats, allowing them to be more easily handled. Thunder Wave allows Lugia to outspeed offensive threats and freely use Roost on them in order to have Multiscale up versus their attacks, making them much easier to deal with. In particular, it punishes Zacian-C, Mega Rayquaza, and Eternatus. Lugia is very passive and so fits mainly on fatter balance teams and stall teams. This is from smogon's article about lugia.
In particular, it is used in hyperoffence teams as a wall to fall back on. In summary almost all teams can use Lugia and its very viable. Here is good set which swept me once-
[email protected] heavy duty boots
EVs252 HP / 252 Def / 4 SpD
you can also use the set given in source
To read more about lugia check out the source!
Hope I Helped!