This assumes you have full control over pokemon generation.
You can (sadly) not set EVs properly in vanilla 3gen.
There's routines on PC you can use if you feel like it,
which allows setting EVs and Nature.
Otherwise, I guess you can just leave it be without.


Based on HGSS team (thus Lapras rather than Espeon)

Pikachu @ Light Ball, Static, Lv88
Mild (204Atk/252SpA/52Spe)
Thunderbolt
Surf
Iron Tail
Substitute


Lapras @ Chesto Berry, Water Absorb, Lv80
Calm (56HP/200SpA/252SpD)
Thunderbolt
Ice Beam
Psychic
Rest


Snorlax @ Leftovers, Thick Fat, Lv82
Adamant (144HP/52Atk/252Def/60SpD)
Curse
Double-Edge
Earthquake
Rest


---- STARTERS ----
Starters are a bit inferior (suggestions below if you want to replace, but I'd retain it)


Charizard @ Lum Berry, Blaze, Lv84
Modest (4HP/252SpA/252Spe)
Sunny Day
Fire Blast
Solar Beam
Hyper Beam


Venusaur @ Leftovers, Overgrow, Lv84
Calm (64HP/64SpA/252SpD/128Spe)
Leech Seed
Sleep Powder
Sludge Bomb
Solar Beam


at this point, we've probably lost -- one last ditch attempt at bringing stuff down
Blastoise @ NeverMeltIce, Torrent, Lv84
Modest (4HP/252SpA/252Spe)
Blizzard
Hydro Cannon
Rain Dance
Signal Beam


Feel free to replace starters with anything below (stronger, but sacrifices vanilla team).
Or just make use of it for some kind of rematch replacing the starters

Metagross @ Choice Band, Clear Body, Lv84
Adamant (252HP/252Atk/4Spe)
Meteor Mash
Earthquake
Rock Slide
Thunder Punch


Gengar @ Leftovers, Levitate, Lv84
Timid (4HP/252SpA/252Spe)
Substitute
Pain Split
Shadow Ball
Thunderbolt


Flygon @ Choice Band, Levitate, Lv84
Adamant (4HP/252Atk/252Spe)
Earthquake
Dragon Claw
Thunder Punch
Crunch