RU is known as The Rarely Used tier. This tier is not made in a way that's competitive but instead aims to be fun which lets low or similar power level Pokemon to be usable, even some usable Legendaries and Megas, which are all mentioned.
Banned Pokemon :
-# Ordered alphabetically, All forms of mentioned mons are banned.
1.) Aerodactyl, Alakazam, Arcanine, Archeops, Annihilape, Archaludon
2.) Barraskewda, Basculegion, Baxcalibur, Bewear, Braviary
3.) Cinderace, Chandelure, Conkeldurr, Copperajah
4.) Darmanitan, Delphox, Dodrio
5.) Dragapult, Dragonite, Durant, Electivire, Falinks, Feraligatr, Flygon
6.) Garchomp, Gallade, Gholdengo, Glimmora, Grimmsnarl, Golisopod, Gyarados
7.) Hariyama, Hawlucha, Haxorus, Hydreigon
8.) Infernape, Inteleon, Jolteon, Kangaskhan, Kilowattrel, Krookodile, Kommo-o
9.) Lucario, Meowscarada, Mamoswine, Metagross, Mienshao, Magmortar, Magnezone, Noivern
10.) Pawmot, Pinsir, Porygon-Z, Primarina, Pyroar, Quaquaval
11.) Revavroom, Rhyperior, Rillaboom, Salamence, Sinistcha, Sirfetch'd, Skeledirge
12.) Slaking, Snorlax, Sneasler, Staraptor
13.) Starmie, Stoutland, Swampert, Talonflame
14.) Tauros, Typhlosion, Tyrantrum
15.) Unfezant, Ursaluna, Volcarona, Wishiwashi
Banned Moves : Venom Drench, Explosion, Self-Destruct Banned. Pure Recovery Moves Banned. 151+ BP Ban. Breeding Moves.
Noteworthy Usable Mons: Includes Unique Pokemon. Check ?tag ru-les
Updates
Special Rules and Noteworthy mons shifted to ?tag ru-les.
Added New Mon : Kubfu, Doublade