The anime-exclusive cards in Yu-Gi-Oh! have never really been consistent in their power, as they are either woefully underwhelming in the likes of Lava and Swamp Battleguard or, particularly when it comes to the protagonist's cards, they are so overpowered that there is no way Konami would ever make them in real life.
There have been some instances where overpowered anime cards have been made into their real-world counterparts, such as the Egyptian Gods and The Seal of Oricalcos, but there are some anime cards than can never make their way to the Yu-Gi-Oh! TCG in the same form they appear in the anime.
10 Slifer Quiz 10
Appearing in the GX anime, Slifer Quiz 10 was just one of many quiz-based cards used by Bob Banter in the Society of Light season. What makes this card stand out from all the other Quiz cards is its ridiculous effect, in which the opponent must complete 20 push-ups within 10 seconds or they take 500 damage. Considering this is a feat that is near impossible for even some dedicated athletes, its almost guaranteed to always go in the favor of whoever played it.
9 Roll Of Fate
This nifty little Spell card has an easy-to-understand effect that has game-changing potential no matter the result and is right up Joey's alley. Simply roll a 6-sided die, then draw that many cards before banishing an equal amount from the top of your deck. At worst, its a better Upstart Goblin, and at best, it will absolutely guarantee whoever plays it is going to win the game, since cards that let you draw usually have much higher drawbacks than this.
8 Virus Cannon
While this card has since made its way to the TCG, it is in a severely altered form to the point that they might as well be two different cards. The real-world version is a Trap card which, at the cost of tributing any number of non-Token Monsters, will force the opponent to send the same number of Spell Cards from their deck to the graveyard.
The anime effect is a Spell card (Trap in the English dub) that sends all Spell cards from your opponent's hand and deck to the graveyard, essentially taking out 1/4 of their deck if it was to be used in the current state of the game.
7 Spell Sanctuary
Used during his semi-finals duel against Yugi in Battle City, Kaiba dropped this during one of his first turns to try and turn the tides in his favor, though it ultimately backfired hard. When activated, it allows both players to add any Spell card from their deck to their hand, and while it remains on the field, both players can activate Spell cards on their opponent's turn. Either one of these effects is overpowered on their own, but combining them into one card elevated it to insane status.
6 The Seal Of Oricalcos
One of the most well-known anime cards in terms of how ridiculous it is The Seal of Oricalcos from the Waking the Dragons filler arc. A field spell that turns any simple duel into a fight for your very soul, as well as having a list of effects almost as long as The Winged Dragon of Ra. When on the field, it can't be targeted or destroyed, allows the player to summon Monsters to their Spell and Trap zones, gives every Monster on their side of the field an extra 500 ATK, and to top it all of, can be discarded from the hand to negate the effect of any card. There is probably a good reason why this card had to be heavily altered before being released in the TCG.
5 Giant Flood
For a long time, Dark Hole was considered the 2nd best option when compared to Raigeki, but when compared to Giant Flood, both of those cards need to be knocked down a peg. For no cost, activating this card will send all monsters on both sides of the field and in both player's hands to the graveyard. While field wiping effects aren't all that common, the amount of effects that take cards from the hand is even fewer, and the ones that are around are pretty much all on the Forbidden and Limited list.
4 Card Of Sanctity
Like The Seal of Oricalcos, this card exists in the TCG, but its effect is so different that it's hard to see where the inspiration for the real world version came from. Used by Yami and Yugi fairly often, this nifty card allows the player to draw until they have 6 cards in hand, being, at worst, Upstart Goblin.
The real-world version is much tamer, forcing the player to banish all cards in their hand to draw 2 and isn't worth the trouble unless players are using a deck solely focused around banishing cards like Gren Maju Da Eiza.
3 Number Monsters
The majority of Number XYZ Monsters have made their way to the TCG since the end of Zexal, but none of them share the anime effect that makes them so powerful. Unlike other XYZ Monsters, the Numbers can't be destroyed by anything other than another Number card, making them a lot like the Egyptian Gods from the original series. While this might not have been as insane back in the peak of XYZ summoning, since nearly every deck used at least one Number card, it's still a protective power that's far too powerful for its own good.
2 Ragnarok
Used by Yugi in the final duel of Battle City against Marik, this card has an absurd cost and activation requirement for the effect it gives. While there are two Dark Magician Monsters on the field, the player banishes all of the monsters from their hand, deck, and graveyard to destroy all cards their opponent controls. Considering Marik had used Raigeki against Yugi in an earlier duel, which does almost the exact same thing, it begs the question as to why Yugi would use this at all.
1 Hundred Eyes Dragon
Also known as the One Hundred Eyed Dragon, this Synchro monster is the epitome of insane anime cards, even when compared to the likes of the Egyptian Gods. Heavily watered down in the TCG, this Dark Synchro not only allows the player to add any card from their deck to their hand if its destroyed, but also copies the effects of every Dark Monster in the graveyard while its on the field. Considering the likes of Jinzo and Dark Armed Dragon are Dark attribute, this could only end in disaster if it ever became a real card.