Yu-Gi-Oh! 10 Powerful Cards So Good They Were Banned!
9. Heavymetalfoes Electrumite
Electrumite was a staple of every pendulum deck up until the 2020 banlist. It was a link 2 psychic monster which required any 2 pendulum monsters to summon, and allowed you to send a pendulum monster from the deck to your extra deck when summoned, destroy one of your scales to add that card to your hand, and then draw another.
It was easily one of the best link monsters in the game due to it's capacity to search almost any pendulum monster and it's cost that required you to destroy a card allowed you to activate the destruction effects for cards like 'Pendulomograph' or other pendulum 'Magicians'. Effectively giving it's controller a card advantage without any drawback, and due to its link arrows, you could pendulum summon it's materials back to the zones it pointed to.
Konami initially limited it to 1 copy per deck, but later banned the card this year due to how it was so easy to summon and with the recent 'Endymion' and 'Mythical Beasts' support for pendulums, it quickly became abused in tournaments as it allowed some of the most degenerate plays.