The flavor text for the card Fat Ass from the parody set Unhinged has the flavor text, "Our lawyers say no matter how funny it would be, we can't encourage players to eat the cards. Hear that? Whatever you do, don't eat the delicious cards."
In an official website article, the author makes a point about the nature of Magic's goblins by offering readers several large red buttons to push. Pushing them (sometimes after several pushes) causes the text and graphics to become scrambled. Except the last button. That one gives a censored preview card for the new expansion.
Whenever your opponent plays something you've never seen before, it's a normal reaction to grab the card for a second to look at it and figure out what it does...Unhinged made this instinctive act come back to bite the player with Vile Bile.
If your opponent has mana available and cards in hand on your turn, odds are they're waiting for you to play something so they can respond to it somehow. Each color has different ways to respond to different cards, but the biggest example is a Blue player waiting for you to spend all your mana to play a creature so they can either counter or return it to your hand.
Trap Cards in general. Your opponent has a completely monster-free field, and you're packing five monsters with 3000 ATK each, ready to bash their brains out. All they have is one measly face down card in their back row. You take the shot, and suddenly you're hit with some ungodly powerful card that completely wipes out your field, and allows them to special summon their 6000-ATK flagship monster for the endgame attack.
My Little Pony Collectible Card Game: The Problem "Fire When Ready" has a 5 point bonus to draw people in, but it's confront requirements are 5 power from each color. Finally, it's effect replaces both Problems when a character so much as moves or enters play there. It is virtually impossible to confront, but it's effect does make it useful.