Red is usually described as a pushover for anyone who knows what he's doing even though he's supposed to be the strongest character in the games. So, hypothetically, if he ever appears in Sun/Moon, here's a team that can make him somewhat of a challenge:

Charizard Y, Level 88
Drought
Charizardite Y
>Fire Blast
>Solarbeam
>Air Slash
>Blast Burn

Venusaur, Level 88
Chlorophyll
Life Orb
>Giga Drain
>Solarbeam
>Sludge Bomb
>Growth

Blastoise, Level 88
Torrent
Assault Vest
>Scald
>Flash Cannon
>Focus Blast
>Ice Beam

Snorlax , Level 86
Thick Fat
Rocky Helmet
>Rest
>Body Slam
>Earthquake
>Sleep Talk

Espeon, Level 85 (Pokemon Sun)
Magic Bounce
Leftovers
>Toxic
>Psychic
>Dazzling Gleam
>Shadow Ball

Umbreon (Pokemon Moon)
Synchronize
Leftovers
>Wish
>Dark Pulse
>Swagger
>Foul Play

Pikachu, Level 94
Hyper Charge
Pikachunium Z
>Volt Tackle
>Iron Tail
>Extremespeed
>Fake Out
>Catastropika

In Gen 7, make it so that recharge moves don't need to recharge if they KO an opponent, that's why Charizard has Blast Burn.

Pikachu has 252 speed EVs and a Jolly nature always. His ability is exclusive to Yellow Pikachu and it acts like a Light Ball.