Like in the original Duel Monsters game, the "Five-Headed Dragon" could not be defeated except by LIGHT monsters
As a reminder, here is the pertinent Oracle text for it: A deck can have any number of cards named Relentless Rats. Well, it seems from the wording, rulings, and rule that it would not be allowed in multiples, but Sheldon, a couple of years ago, made this post in the forums: The RC has discussed it and for the time being thinks that multiple Rats is OK
Released in 2004, the expansion highlights Regirock, Regice, Registeel, and Jirachi as well as several strong Pokmon-ex like Metagross and Registeel
Cipher Etranger Chinese name: Cipher Etranger Cipher Etranger (OCG) Cipher Etranger (anime) Cipher Etranger (OCG) Japanese name: Cipher Etranger English name: Cipher Etranger Password: 79094383 Card type: Effect Monster Limitation: Unlimited Level: 1 Attribute: LIGHT Type: Spellcaster ATK: 0 DEF: 0 Rarity: Normal Card Pack: RATE(911), 21TP OCG Effect: 9th-10th Period Effect Text: You can only use 1 of this card name's or effects per turn, and only once that turn