Here's why it was banned and how it used to be played:
* Overpowered Effect: "Chthonian Emperor Dragon" had the ability to banish any number of cards from your graveyard and then, for each card banished, destroy a card on the field. This was incredibly powerful and could easily clear the field of opponents' monsters and spells.
* Easy Summon: While it has a high attack stat (3000), it was relatively easy to summon, using only 2 monsters with a combined level of 7.
Here's how it would have been used in the past:
1. Summoning: Summon "Chthonian Emperor Dragon" by using two monsters that combined have a level of 7.
2. Banishing and Destruction: Banish cards from your graveyard. For every card banished, destroy a card on your opponent's field (either a monster or spell/trap).
3. Control: Use the card's powerful effect to clear the field and gain a massive advantage.
Important Note: "Chthonian Emperor Dragon" is no longer allowed in official tournaments and most casual play because of its sheer power.
If you're interested in playing Yu-Gi-Oh!, there are plenty of other amazing and powerful monsters to explore! Check out the official Yu-Gi-Oh! website or card database for the latest rules and card information.