RBY Quirks

Alakazam
No Items, Abilities, EVs, or IVs.
Instead of Special Attack and Special Defense, Pokemon have a single "Special" stat that can be boosted by Amnesia.
Critical hits ignore all stat changes from both the user and target. Crit chance is calculated based on the user's Speed (faster Pokemon have a higher crit rate).
Frozen Pokemon never thaw.
Confused Pokemon have 1/2 chance to attack each turn.
Paralyzed Pokemon have a 3/4 chance to attack each turn.

Jolteon
In Gen 1, recovery moves fail if (user's maximum HP - user's current HP + 1) is divisible by 256.
https://replay.pokemonshowdown.com/gen1ou-1410870380-778xnno6u1pv7vg9cuz6bbjnbgk7ndhpw Turn 35
Substitute blocks Toxic and Confuse Ray.
Substitute does not block Thunder Wave, Leech Seed, Super Fang, Disable, Transform, Bide, Counter, Rage, Haze, or the secondary effect from moves like Body Slam or Confusion if they break the Substitute.
If a Pokémon breaks a substitute with Hyper Beam, it will not need to recharge. If a Pokémon breaks a substitute with a recoil move, it will not take any recoil damage.

Exeggutor
Leech Seed's damage ramps up each turn vs a Toxic'd opponent, and continues increasing even when Toxic is removed with Rest.
Psychic has a 33% chance to lower the target's Special.
Thunder only has a 10% chance to paralyze.
Fire Blast has a 30% chance to burn.
Rock Slide has no additional effect.

Gengar
Disable has 55% Accuracy and lasts 0 - 7 turns.
Mimic replaces itself with a random move known by the target.
Night Shade can hit every type, including Normal.
Seismic Toss and Super Fang can hit every type, including Ghost.
Counter only works against Normal and Fighting type moves.

Zapdos
RBY 1v1 does not exist yet as a challengeable format on PS! To play this metagame, send your opponent the [Gen 1] 1v1 Challenge Code:

/chall gen1ou@@@ -uber, max team size=3, picked team size=1, -Hypnosis, -Lovely Kiss, -Sing, -Sleep Powder, -Spore, -Explosion, -Self-Destruct, -Flash, -Kinesis, -Sand Attack, -Smokescreen, -Wrap, -Bind, -Fire Spin, -Clamp, teampreview