Hosers
Most cards in trading card games make yourself more likely to win, less likely to lose, or interfere with what your opponent is trying to do. Hoser cards are a little different. They don't help you win or keep you from losing, and unless your opponent has a specific type of deck, hosers won't do anything to them either. But if your opponent does have the type of deck your hoser counters, it utterly destroys them.
For example, the card Drought from Magic the Gathering forces the opponent to sacrifice lands every time they need to spend black mana for something. Against a deck that has no black mana costs, this card is useless. Against a mono black deck, this card is more or less a guaranteed win assuming you can cast it and your opponent can't get rid of it.
There are two main issues with hosers. Firstly, getting one off against the right opponent is a guaranteed win under normal circumstances, but it doesn't actually end the game. This can result in lame duck scenarios where one player can't do anything but isn't technically dead yet. They could forfeit, of course, but there's no rule that says they have to, and if they're feeling stubborn they can drag the game out for no reason, which isn't really fun for either player.
The second reason is that they have the potential to give a player a win at no cost and no risk. Just putting a hoser card in your deck is a horrible idea normally, because it will be worthless against most of the opponents you play against. But you don't have to put the card into your deck. You can put it into your side deck and just slot it in if your opponent is playing a deck that's vulnerable to your hoser and enjoy your free win. The only cost for this is side deck space, and some types of decks don't really need their side deck for anything. At best, this situation results in a player winning without having to apply any skill when playing or any thought when deckbuilding. At worst, this can result in entire types of strategies that could otherwise be viable going by the wayside because they are so easily countered by hoser cards.
Because of these reasons, card game design has mostly moved away from hosers. Instead, most card games nowadays will print cards that do something in all situations but are powerful against specific decks without maiming them outright. An iconic example of a card like this would be Jinzo from Yu-Gi-Oh. Against a deck with no trap cards in it, Jinzo is still a monster with reasonable stats for its level, and can help you out by damaging your opponent. Against a deck that relies on trap cards he can be a serious pain, but he has no protection. The opponent can remove him with a spell, a monster effect, or a stronger monster, but until then they can't use traps. Jinzo counters traps, but doesn't hose traps.
However, hose cards are still occasionally printed in modern card games. The main reason is that they can serve as a tempting alternative to banning cards from a problem deck. For whatever reason, most card game designers see admitting a card was a mistake and banning it as a level of humiliation somewhere between starring in a bukkake shoot and being caught having sex with a chihuahua (receiving) during a bathroom break at the latest Future Future League. They'll fucking eat a card before banning it, no matter how obviously broken it is. Hosers provide a way out. The idea is to make the broken deck worse not by banning cards but by making them lose games at random to hosers. What actually happens is that everyone is forced to run those hose cards instead. So instead of Good-Deck-A, Good-Deck-B, and Good-Deck-C, everyone is left with a situation where they have to play Broken-Deck-X or Hoses-Broken-Deck-X, or lose.
If you're a card game designer, or maybe just putting together a cube, and you're considering adding a hoser, there's three questions you should ask yourself first:
- Is this card fun for the player who's playing it?
- Is this card fun for the player who's getting hosed by it?
- Does this card create interesting deckbuilding decisions?
If the answer to more than one of those questions is no, you probably shouldn't put that hoser in your game. If one strategy is too powerful, tone it down, or add cards that counter that strategy without warping the game around it.