Yu-Gi-Oh! 10 Powerful Cards So Good They Were Banned!
2. Destrudo The Lost Dragon's Frisson
Destrudo was a Dark Lv7 dragon tuner monster which could special summon itself from the hand or graveyard by paying half of your life points to target a Lv6 or lower monster you control and reduce it's level by that targeted monsters level and placed itself at the bottom of the deck when it left the field.
The card was used consistently in most decks as it could be easily sent to the graveyard with cards such as Foolish Burial or Dragon Shrine. By changing its level on summoning, it could instantly synchro summon any Lv7 synchro monster if you had another monster on the field. And as it could be used from hand or grave, it could be used to discard for a cost and still use its effects However, the reason it got banned was that it was basically a "free card" as life points didn't matter if it enabled an OTK or gave such an immediate advantage.
It could be summoned easily and provided access to a myriad of Lv7 synchros like Dragster or used for link summoning Guardragons, or even in pendulum decks to Xyz summon Absolute Dragon. Therefore forcing Konami to hit it with the ban-hammer.