Fail is right. Now that I get this uses CYOTCG rules, we should probably repost them:
Game Rules
1) You start off each game with 20 hearts, and 5 cards in your hand. For any given game, you and your opponent may decide to start with a different amount of any of those three things.
2) If you have 0 or less hearts, you lose.
3) At the start of each turn, you draw one card.
4) Unless stated otherwise, you can only play one card per turn.
5) Cards also have hearts. If they have 0 hearts, they go away, unless stated otherwise. If a card says it has attack power, it can only damage the player directly if they have no cards defending them.
6) If a card has zero hearts when you play it, it will be destroyed after it does its effect.
7) There is a kind of resource called Stars, and you start the game with 0 of them. Strong Cards cost Stars to play, and they can be gained with the effects of weak cards. This prevents your best cards from being played immediately. Cards may also have effects that cost stars to use. (Stars carry over between turns)
The player who goes second starts the game with one star.
9) You can also make up your own resources for your cards if you really want.
10) Cards cannot attack on the turn they are played unless otherwise stated, and can only attack once per turn unless otherwise stated. When a card attacks another card, both cards lose hearts equal to the other card's attack
11) By default, if a card is face down it cannot be attacked. Cards may be attackable when face down, in which case this must be declared when playing the card.
12) Face Down cards cannot protect you from being attacked until it is flipped up. If a facedown card does something it will be flipped.
13) The game will typically use the honor system, so players can randomize their own deck and draw cards without GM intervention. If you suspect someone is cheating, inform the GM. Its just sad if you feel the need to cheat in this game. For grudge matches, you can request the GM do all the random stuff.
14) Strive to avoid situations which will require a retcon. Those are a big pain to clean up.
15) In the event of a disagreement, the GM will decide what happens.
16) Don't be afraid to get creative with your deckbuilding!
17) If a card says it does something "At the end of each turn", this only means your own turns unless it specifically states otherwise.
Relative card strength
A card that costs no stars to play would typically have a combined stat total of 5. (Example, 2 attack and 3 hearts). Useful effects will generally lower this, and detrimental effects can raise it. You can also make cards with no hearts which act like "Spells". Each star a card costs will typically raise its base stat total by 3 or 4. Very high star costs can have ridiculous effects.
Tips
Cards can do all kinds of things if you want them to! Want to attack on the turn a card is played? You can give it an effect to let it do that. Don't like only playing one card per turn? Make some cards that don't count towards the limit, and some other cards that let you draw more cards!
You'll want to consider your "Star economy". You can have just a few cards with a very high star cost, or maybe an equal amount of star generators and star consumers. Or maybe just skip the stars altogether and have a lot of basic cards.
You can give cards effects that trigger when they are destroyed, when they attack, when they are attacked, when played alongside another card, cards with an effect depending on how long the game has been going on for, or any number of things really. Surprise me!