N'Synch
Famous for its loops, this is the only signer dragon on the forbidden list
Ancient Fairy Dragon
This archetype is based on the Draco constellation, which includes stars such as Thuban, Aldhibah, and Fafnir
Drytron
This fusion spell was one of, if not the first cards to let you use your deck as fusion material.
No one knows what this card does
Pot of Greed
Link Tokens
Linkross, Link Devotee
This card was one of the earliest level 9 synchros and was so powerful, they named a pack after it.
Trishula, Dragon of the Ice Barrier
This archetype draws inspiration from the mythical golden city, El Dorado
Eldlitch
Famous for its use in a wide variety of decks, most notably 60 card, this is the only forbidden fusion spell card.
Brilliant Fusion
Although not as infamous as its counterpart, this monster has given many Ls due to its crazy BS.
Black Luster Soldier - Envoy of the Beginning
Fluff Tokens
Dandylion
Ursarctic Polari
This WIND archetype has Greco-Roman-inspired main deck monsters and synchro monsters named for legendary weapons
Dragunity.
This card saw play in the ocg as a way to make Red-Eyes Dark Dragoon and is the only Synchro monster in the game that lets you fusion summon
Muddy Mudragon
Known for its use with a limited spell card, it was actually properly summoning this card and looping it that got it banned.
Elder Entity Norden
Phantasm Spiral Token
Pacifis, the Phantasm City
The corrupted counterpart of another synchro monster, this card has the same stat line, but has a different attribute and is one level higher. Its powerful effect compensates for its restriction to pendulum strategies.
Supreme King Servant Dragon Clear Wing
This archetype is based on the solar system. Their boss monster is named for the Greek titan of the sun
Agents
The fusion spell for Burning Abyss, this card summons Purple Dante
Terminus of the Burning Abyss
This monster famously killed Weevil 7 times over
Breaker the Magical Warrior
Skyblaster Token
Phantom Skyblaster
Guardragon Agarpain made this card's counterpart famous, but this level 10 synchro has a powerful revival and swarm effect. It didn't merely adopt the extra deck. It was born in it.
Hot Red Dragon Archfiend Bane
This relatively new archetype has xyz monsters inspired by the 4 Symbols of Chinese mythology: the Azure Dragon, the Black Tortoise, the White Tiger, and the Vermillion Bird, although the Tiger does not exist yet
Virtual World.
Many fusion monsters require specific cards to summon them, but this is the only one that actually fusion summons its monsters.
(I.E. Must be Special Summoned with _____.")
Dark Fusion
Forbidden for a brief period from 2008-2009, this continuous trap card wasn't put back to 3 until 2012.
Call of the Haunted
Battle Eagle Token
Number 42: Galaxy Tomahawk