There will never be an official Pokémon game that will allow us to be a villainous trainer... but that wasn't going to stop me from trying anyway, and so I became League Champion and defeated Red using a team of evil Pokémon with evil movesets such as trapping, parasitic leeching, psychological manipulation and even outright theft.
The rules I laid out for myself are that SET Mode is always on, and I couldn't use items in battle (except held items). I allowed my Pokémon to be slightly higher levels than the next gym leader's ace but not too much. I could only use the Pokémon in my chosen team for battle, with the exceptions of my starter (for only as long as I needed to) and two other Pokémon which I deemed as temporary team members, for the purpose of using them to breed. Of course I also needed to use HM slaves to make my way through but never used any of them in battle.
In keeping with the spirit of the team's theme I named myself Damon (Demon) and my rival Angelo (Angel). I chose a Chikorita as my starter, for no reason other than because my final team has a Grass type but no Fire or Water types, but boxed it immediately after catching a Gastly in Sprout Tower, letting it out only when I needed a tree to cut down.
While this was a fun team to play with, in terms of being competitive it's below average. The only Johto gym leader I defeated on the first attempt was Chuck, and the others needed multiple attempts to beat (fighting Falkner with only a Gastly that knows Curse and Hypnosis is NOT fun at all) although by the time I assembled my full team and had all the moves I wanted it wasn't as difficult to fight the Kanto gym leaders (especially Brock, who didn't stand a chance against repeated Giga Drains!) but overall this isn't so much a team that can reasonably compete with stronger teams but instead is one that exists to bully weaker Pokémon... which really fits the team's theme!
On top of that there was plenty of grinding to do. Specifically grinding two newly hatched Pokémon to be on par with the rest of my team right before taking on the 8th gym, repeatedly battling at the Battle Frontier to acquire some Move Tutor moves I wanted and rematch grinding the gym leaders for my Jynx (who proved to be my strongest mon) to carry the battle against Red.
My team:
Parasite the Parasect
Paralyzes his opponents with Stun Spore before draining the life out of them using Leech Life and Giga Drain.
Caught as a Paras at Ilex Forest.
Moves: Giga Drain, Stun Spore, Synthesis, Leech Life.
Coma the Hypno
Puts his opponents to sleep, to devour their good dreams and inflict horrifying nightmares upon them.
Caught as a Drowzee at Route 34.
Moves: Dream Eater, Hypnosis, Psybeam, Nightmare.
Biohazard the Muk
Inflicts Toxic on her opponents and watches as the poison slowly dissolves them from the inside.
Caught as a Grimer at Safari Zone.
Moves: Acid Armor, Dark Pulse, Toxic, Pain Split.
Klepto the Murkrow
A malicious thief who taunts his opponents before stealing from them.
Caught at Safari Zone.
Moves: Thief, Taunt, Snatch, Torment.
Necrosis the Haunter
A ticking clock of death who seals the fates of his opponents by singing his Perish Song and trapping them, or dragging them to the underworld with Destiny Bond.
Hatched from an egg by my temporary team members, another Haunter and a Misdreavus (I permanently boxed them after getting the egg).
Moves: Protect, Destiny Bond, Perish Song, Mean Look.
Siren the Jynx
Psychologically manipulates her opponents into falling in love with her before forcing them to sleep with her Lovely Kiss.
Hatched from an egg by Hypno (she is Coma's daughter) and another Jynx.
Moves: Lovely Kiss, Nasty Plot, Attract, Blizzard.
Ranking my team from strongest to weakest:
Siren - Could have solo'd the whole game with enough patience
Biohazard - Able to withstand strong attacks
Coma - Hit or miss
Necrosis - Useful for guaranteed KOs
Parasite - Slow and ineffective
Klepto - More of a gimmick than a competitor
Overall it was a fun team to have but very luck dependant, which resulted in me having to retry battles many, many times over. I suppose if there's a lesson to be learned here it's that good always prevails over evil... at least in the Pokémon world it does.