Yu-Gi-Oh! 10 Powerful Cards So Good They Were Banned!

Rhongomyniad was an Xyz monster which gained different effects that stack based on the number of materials it has. With 1 it could not be destroyed by battle. 2 doubled its attack and defense. 3 materials granted it immunity to all other card effects. 4 materials stopped your opponent from normal or special summoning monsters. And with 5 materials, you could destroy all cards your opponent controlled.

It's drawback however was that during your opponent’s End Phase, you had to detach 1 material each turn. With the effects of other Xyz monsters which could attach themselves to him it coined the term RhongoBongo whereby it became an almost unstoppable 3K attack behemoth. After making Rhongo using Lv4 monsters as material, use Phantom Knights to swarm the field with Lv3 monsters and summon Gossip Shadow which would then attach itself, and all of its materials, to Rhongomyniad which would give it up to 7 materials.

Rhongo would then wipe the field and could stay on the field for multiple turns and win the duel with ease forcing Konami to ban it to appease players on the receiving end of what was considered a completely broken play as it had almost no counter.