The competitive rules to Yu-Gi-Oh! are a bit different compared to other trading card games. That is because any card in the game can be used in a tournament-legal deck (assuming it is not on the banlist) rather than using Set rotation (meaning only the latest Sets are legal). This means you can use the very first card ever released in a modern deck if you wanted.
With this in mind, many old cards are still used to this day despite twenty years passing since the first set. On the other hand, old cards that were once so good they had to be banned have had the opposite effect. Rather than keeping their strength, they've been power-crept to the point where they're useless in the modern game.
Updated November 29, 2021 by Johnny Garcia: The game of Yu-Gi-Oh! has constantly evolved ever since its inception. Cards printed in the earliest Sets can suddenly become amazing, whereas cards that were once dominant forces can become nothing more than a gimmick. This is largely thanks to the sheer amount of Sets that have entered into the game yearly. Recent Sets like Burst Of Destiny and Ghosts From The Past have provided players with a plethora of powerful cards that have completely shut down any chance of older cards being played thanks to the immense levels of power creep. Power creep has shown no signs of slowing down, and it likely won't anytime soon.
10 Summoned Skull
Summoned Skull was once one of the biggest threats in the earliest format of Yu-Gi-Oh. For one tribute, a 2500 attack monster was some of the best value you could get. Nowadays, monsters that require a tribute are simply too slow to be good.
Not only that but Normal Monsters have little to no use in the modern game. Summoned Skull would have its own archetype built around it due to its popularity, but that was far from enough to bring Summoned Skull to viable levels. Summoned Skull went from being a card in everyone's deck, to not being in any decks at all.
9 Call Of The Haunted
Call Of The Haunted was a card so good in the earliest formats that it was limited on the first-ever banlist, and eventually banned for some time. Currently, Call Of The Haunted is unlimited and has been since 2012. This is attributed to the game becoming faster, and Trap Cards become more obsolete.
Call Of The Haunted has to be set, and can't be used until after your turn ends. It simply takes too long for its effect to come in handy, so it's not on any radar when cards like Monster Reborn exist that are strictly better versions of it.
8 Fissure
Fissure was the first removal Spell that was released in Yu-Gi-Oh! It was instantly a staple in every deck, and one of the few ways to catch up to the opponent if they got a board going before you had much of a board presence. In fact, it was so good it was limited from 2007 to 2009.
Fissure was always doomed to fall off, however. The card can only target the Monster with the lowest Attack, and it was eventually power crept by cards that could either target the highest Attack Monster, or just any Monster in general.
7 Magic Cylinder
Magic Cylinder was once one of the powerful Trap Cards in the game to the point it had to be limited on the very first banlist. It would stay there until it became semi-limited in 2010 and eventually unlimited in 2012 where it would stay.
Magic Cylinder can negate an attack and then inflict damage to the opponent equal to the attack of the monster whose attacks were negated. The fall of Magic Cylinder was due to the fall of Battle Traps in general since many decks can get rid of the cards before the Battle Phase even begins. It also targets, which many big monsters are immune to in the current metagame.
6 Swords Of Revealing Light
Perhaps the most iconic Spell card in the entire game, Swords of Revealing Light used to be one of the best stall cards. Its effect would prevent your opponent from attacking for three turns. It also flips all face-down monsters your opponent controls up. This effect was so good, it was limited on the first banlist, and stayed there until 2012 when it was taken off.
Many more cards and Monster Effects exist in the game now that can very easily get rid of Swords Of Revealing Light since it has to stay on the field for the effect to be active. This keeps Swords Of Revealing Light off anyone's radar, especially when a card much better than it exists in Mystic Mine.
5 Nobleman Of Crossout
Nobleman Of Crossout was the premiere removal card in the earliest days of Yu-Gi-Oh! Since there was much more setting of Monsters, Nobleman Of Crossout was the main way to get rid of them to ensure their effects never activated. If it was a Flip Monster, all copies of it would be forever gone from the game.
As the game got progressively faster, setting a card became much less common, to the point Nobleman Of Crossout is dead in the hand more often than not. The card became iconic and even got an upgraded retrain in Crossout Designator.
4 Mirror Force
Mirror Force is one of the most iconic cards in the entirety of Yu-Gi-Oh! for both casual and competitive players alike. Its effect would destroy all of your opponent's attack position monsters if they declared an attack. Mirror Force was so powerful it would spend its early life on the banlist as limited (and straight-up banned for a few formats) before eventually becoming fully unlimited in 2014. Like Magic Cylinder, Battle Trap" would stop seeing much play, and that included Mirror Force.
Not only that, but many Monsters are also immune to destruction from card effects now, or have effects that activate when they get destroyed. As such, Mirror Force has become irrelevant. Although, other forms of Mirror Force do see some play, such as Storming Mirror Force. So while Mirror Force has become useless, its legacy continues to live on.
3 Exiled Force
Exiled Force, at one point in the Yu-Gi-Oh! meta, could do it all. It could deal a decent 1000 points of damage, but it shined with its effect. Exiled Force could destroy any Monster in the game with its effect, and thanks to Priority Rules in the early day, there was almost nothing the opponent could do to stop it short of a Solemn Judgement.
Exiled Force was searchable as well, making it one of the most consistent outs to any Monster. It spent some time limited before coming back into a much faster meta, and it could never catch up to the speed of the modern game.
2 Breaker The Magical Warrior
Breaker The Magical Warrior spent its time in the meta as the best Normal Summon in the entire game. In the earlier days of Yu-Gi-Oh!, Spell and Trap cards being set were much more common, so having a strong body that could also deal with them was one of the best effects in the game. Breaker The Magical Warrior spent time both limited and banned, before becoming unrestricted in 2009.
As the game progressed, better Normal Summons with better stats were released, as were better ways to combat Spell and Trap cards. After Breaker The Magical Warrior fell off, it never found a home in the meta again due to how outclassed it was by the competition.
1 Spirit Reaper
Spirit Reaper is such a good card, it formed an entire format around it after GOAT, fittingly named Reaper Format. Spirit Reaper was once an incredibly hard card to get rid of, with targeting it being the only reliable way to do so. It was the perfect stall card, and if you were in a good position it could even rip cards out of the opponent's hand.
Spirit Reaper spent a long time on the banlist as Limited, and by the time it came off its time had passed. Many other cards took its place, and Spirit Reaper lost its home in the meta.