Game Breaker/Card Battle Game

• Exodia in Yu-Gi-Oh!: 7 Trials to Glory. The game has a special area in which there is no banned/limited list, which means you're not only allowed three separate copies of each Exodia piece in your deck, you're allowed three copies of Sangan and Witch of the Black Forest to search them out, AND three copies of Dark Hole, which destroys all monsters on both sides of the field, nuking the opponent's offense while allowing your searchers to do their job. There is also access to 3 copies each of Pot of Greed and Graceful Charity, which all together accounts for fifteen cards with essentially no penalty. The in-game currency reward system has a strong bias towards winning through non-standard means (and Exodia is considered non-standard); what this means is that you get ten times the normal winnings for performing poorly. You can even buy a Deck that is pre-made with all the above cards.
• In Yu-Gi-Oh! Reshef of Destruction: The Winged Dragon of Ra's Phoenix Mode can be discarded in the hand, to immediately appear on the field in Battle Mode. ^[1]
• Sevens, Rosemon Lures and Download Digivolve in Digimon Card Battle, all of which counts as Infinity+1 Sword.
  • Digimon support are another, since some effect are exclusive to them, and some are ridiculously powerful. Rare types in general have lots of it, who have several number manipulation ability, most notably Toy-Agumon, that make the entire game a breeze.
• Yu-Gi-Oh!: The Sacred Cards had an absurd number of these...so many that the difficulty comes from trying to determine which of these are the most game-breaking. To give a few Egregious examples:
  • Darkness Approaches. Rather ironic, as the real-life card game version is considered one of the worst spells in the game, but there's no denying how utterly game-breaking the SC version is. It turns all monsters on your whole field face-down for no cost at all, allowing them to re-use their instant Flip Effects - a great many of which are clearly meant to be used once per card. One extreme example is Revival Jam, a card that copies itself when activated. Not game-breaking by itself, but with a single Revival Jam and a single Darkness Approaches, you now have four Revival Jams on your side of the field ready to pounce.
  • Hourglass of Life. It powers up every monster on your side of the field by 500 attack and defense points. Permanently. Not only is this a Game Breaker by itself, but combine it with the above Darkness Approaches and Revival Jam tactic, and you now have two 2500 ATK and two 2000 ATK Revival Jams (not to mention the now 1700 ATK Hourglass itself) in practically no time at all. It is possible to, with the right combination of Hourglass of Life, similar attack boosts, and Darkness Approaches, get a full field of garden-variety monsters to over 4000 ATK, without ever needing any tributes. To call this a One-Hit Kill is an understatement.
    • The lesson of just how game-breaking these sort of attack boosts are is taught to the player very quickly via Witch's Apprentice, a card the player starts with. It works like Hourglass of Life, except it only powers up Shadow-element monsters. Which in itself is overpowered, because of how the game's Elemental Rock-Paper-Scissors works. In theory, it's Shadow > Light > Fiend > Dreams > Shadow. The problem with this is that Dreams-element monsters are ridiculously rare, to the point where encountering one in the entire game is an event unto itself, making Shadow an unintentional Infinity+1 Element. And on the off-chance that you do encounter such a monster...well, that's what your trap cards are for.
  • Torrential Tribute, which instantly wipes out every single monster on the opponent's field the instant they try to attack with absolutely anything. And unlike the real-life game, where Mirror Force (a WEAKER version of said card, as it doesn't hit face-downs) is limited to one, you can have three Torrentials in your in-game deck.
    • For that matter, almost any trap card in the game, because the AI is stupid enough to attack every time it has a chance to win that particular battle. This definition of "chance" includes your face-down monsters. All you need to do is the following: set trap, set monster, end turn, laugh as the opponent kills themselves, attack with all face-up monsters, and repeat until you have won the duel. Traps like Invisible Wire (kills anything under 2000 ATK that attacks you, which no enemy except the final boss can summon without a tribute), Acid Trap Hole (everything under 3000 ATK), and Widespread Ruin (just everything) make the game insultingly easy. To make matters worse, these cards have a deck cost that is absurdly low; deck cost acts sort of like your Character Level, determining the relative power of your deck. Widespread Ruin costs less than the local Goombas to put in your deck, and the other traps cost even less than that. Only Torrential has anything even vaguely resembling a real cost...which you can still pay at the very beginning of the game with minimal effort.
• Lost Kingdoms can be broken by ignoring the maximum deck size and instead making a small deck comprised of nothing but the most powerful attack cards you have and "recover used cards" cards.

1. ↑ It doesn't necessarily guarantee a win, though, if your opponent can lower its Attack/Defense Points with Effect Cards.