Its Bugs time! Never have the time to play this Meta but always have it to introduce some chaotic submissions.

Name: Parasect
Stats: 74 HP (+14), 95 Attack, 87 Defense (+7), 84 Special (+4), 31 Speed (+1)
Typing: Bug/Grass
New Moves: Counter, Seed Bomb.
Removed Moves:
Signature Move Name: Seed Bomb
Type: Grass
BP: 100
Acc: 100
PP: 8
Effect: User faints. During damage calculation, the Special Stat of the opponent is halved.
Parasect still has the crappy Leech Life as the only Bug STAB. However, now it can explode with Seed Bomb. Seed Bomb OHKOs every Mon weak to Grass and damages Tauros really hard too. Its still a very humble Mon with bad Stats, but now it can sleep one Mon and eliminate or weaken another. Counter is another new Move to have an extra surprise KO for something like Snorlax (which Parasect now outspeeds by one point).

Name: Butterfree
Stats: HP 70 (+10), Attack 45, Defense 85 (+35), Special 90 (+10), Speed 80 (+10)
Typing: Bug/
Psychic
New Moves:
Silver Wind, Recover.
Removed Moves:
Signature Move Name:
Type: Silver Wind
BP: 60
Acc: 85
PP: 16
Effect: Partial trapping move (like Fire Spin).
Butterfree now has the strongest partial trapping Move and strongest Bug move in general, capable of 2HKOing Exeggutor, Victreebel, Venusaur and Jynx. However, it still comes from the terrible
45 Attack, meaning that the rest of the meta will be taking the move very well. For example:
Butterfree Silver Wind vs. Aerodactyl: 25-30 (6.8 - 8.2%) -- possibly the worst move ever
Butterfree Silver Wind vs. Snorlax: 54-64 (10.3 - 12.2%) -- possible 9HKO
Butterfree Silver Wind vs. Chansey: 113-133 (16 - 18.9%) -- possible 6HKO
Butterfree Silver Wind vs. Cloyster: 28-33 (9.2 - 10.8%) -- possibly the worst move ever
Butterfree Silver Wind vs. Charizard: 12-15 (3.3 - 4.1%) -- possibly the worst move ever
Fortunately for our little Bug, thats not all, it now also gets the Psychic typing and like many Psychics, it learns Recover too. This makes Butterfree a good Psychic and Fighting check. Despite 65 BST increase, Butterfree still has pretty lackuster Stats, so like every Mon in this post, it has an important niche that comes with very important drawbacks. Bug Mons are designed for Bug Maniacs, not everyone will be capable of using them well, but those who do, will finish the Psychic reign.

Name: Venomoth
Stats: HP 70, Attack 88 (+23), Defense 84 (+24), Special 90, Speed 90
Typing: Bug/Poison
New Moves: Sludge,
Quiver Dance, Recover
Removed Moves:
Signature Move Name: Quiver Dance.
Type: Bug
BP:
Acc:
PP: 32
Effect: Raises Special and Speed one stage.
Like Parasect, Venomoth still has a very bad typing, however the Stats and movepool improve a lot. Sludge allows Venomoth to 4HKO Chansey, with a chance of poisoning it too. Quiver Dance makes Venomoth a very unique sweeper, especially if its combined with Recover. A well played Venomoth with Quiver Dance, Sludge/Sleep Powder, Psychic and Recover can win vs the whole meta. Key word here is well played, cause the Stats and Psychic weakness balance this Mon:
Alakazam Psychic vs. +1 Venomoth: 173-204 (50.4 - 59.4%) -- guaranteed 2HKO < So, Alakazam paralyzes Venomoth and pretty much wins.
Snorlax Body Slam vs. Venomoth: 110-130 (32 - 37.9%) -- 95.6% chance to 3HKO < Better match-up, especially if Snorlax is asleep, but para still can ruin the moth.
+1 Venomoth Psychic vs. Aerodactyl: 114-135 (31.4 - 37.1%) -- 84.7% chance to 3HKO
Aerodactyl Rock Slide vs. Venomoth: 190-224 (55.3 - 65.3%) -- guaranteed 2HKO < Counter right here.
+6 Venomoth Psychic vs. Starmie: 108-128 (33.4 - 39.6%) -- guaranteed 3HKO < Another counter if it has TW + Psychic.
Dangerous as Venomoth is, it needs a lot of the meta to be removed, weakened or statused before attempting to sweep, since Poison typing hurts more than it helps, even with Sludge.

Name: Scyther
Stats: HP 70, Attack 110, Defense 80, Special 80 (+25), Speed 105
Typing: Bug/Flying
New Moves:
Acrobatics, Counter
Removed Moves:
Signature Move Name: Acrobatics
Type: Flying
BP: 55
Acc: 100
PP: 24
Effect: Nearly always crits.
Instead of being a poor Mon walled by Gengar, Scyther is now an extremely dangerous breaker with a powerful Flying STAB. It also resists special hits better now.
List of common RBY Mons that are 2HKOd by Acrobatics: Gengar, Alakazam, Exeggutor, Chansey (88% roll), Victreebel (30% to OHKO), Venusaur, Beedrill ( 100% OHKO with the new Stats), Flareon, Machamp, Abomasnow, Medicham (2% to OHKO), Plucks, Sneasler (60% to OHKO), Persian, Jynx.
List of common RBY Mons that are not 2HKOd by Acrobatics and are NOT Flying resists: Tauros, Snorlax, Starmie (0,2 % to 2HKO, miserable), Slowbro, Cloyster (4HKO, so pretty much a counter), Dewgong, Armaldo, Talonflame.
Scyther counters: Every single Rock type except Armaldo stop it cold (Armaldo is 3HKOd, so still decent enough). Cloyster is also a full stop, and ice moves in general work well. Talonflame outspeeds Scyther, and Aerodactyl obviously is the best counter of them all. Electric types are good checks, but not full counters, since Slash and +2 Hyper Beam has a chance to KO Zapdos (due to the increased Special, Scyther now always lives a Tbolt from full). Jolteon does outspeed, but does not OHKO either and is OHKOd 71% of the time by +2 Hyper Beam.
Still, Scyther will be a hard to use Mon, but a dangerous threat when supported well enough. Like already said, common theme for all the Mons in this post.