Scyther

Scyther @ Choice Band
Ability: Technician
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- U-turn
- Aerial Ace
- Brick Break
- Knock Off
Choice Band
Scyther fits very well together with Rotom-Frost as
Rotom-Frost can remove hazards, which will potentially trouble Scyther, such as Stealth Rocks whereas Scyther can help with the wallbreaking from Rotom-Frost.
CB Scyther removes threats such as Tangela, Lurantis and Gurdurr, same goes to Hitmonchan and Primeape with its good STAB options in U-Turn and Aerial Ace, whereas Rotom-Frost might struggle with due to priority-moves from them
or due to a higher speed-tier or the specific Set they run.
Furthermore it removes Probopass and Alola-Sandlash with its Brick Break coverage, which are troublesome for Rotom Frost because it might have trouble to break through these threats.
To add onto that Knock Off is a good option here as well because it can remove the longevity of bulkier threats such as Mudsdales Leftovers, it can also remove the items of a incoming Lanturn.
In Return Rotom-Frost can threaten pokémon pretty well, which might be a problem for Scyther such as Mudsdale or Qwilfish because Ice/Electric coverage is really good and hits most pokémon in this tier to help Scyther out.
Rotom-Frost can also help against Poliwrath because Scyther has to fear a burn which limits its breaking potential, Carracosta can also be a bit troublesome for Scyther, but Rotom Frost can take care of it
as well because the electric-type STAB does a big damage to Carracosta.
These 2 pokémon in generall can form a nice Volt-Turn core to bring other team-mates in safely due to U-Turn and Volt Switch giving the team-mates Momentum.
Also U-Turn and Volt-Switch from both will chip away incoming pokémon, which is really appreciated and important in the long run of a game.