Fun, ebc should totally set up a card suggestion forum.
My thoughts.
1) You hit a girl. Haha, funny. An alternative is to have "You hit a nerd" and have some dude in glasses, and if a female hits him, then the same effect. Does anybody know offhand the ratio of "guy cards" to "girl cards"? And am I the only one who thought "Blade Master" was a girl for a few weeks before looking a little closer?
2) Devil Dice. Creative, but 3 times in a row? That would need a pretty low count-down, or it wouldn't really trigger all that often. Even at 7 seconds, you have to get 21 seconds into a game for a chance of it activating, and only gaining 6% increase. That attack power increase gold card (forgot the name, too lazy to look it up) gives you a lot more and is guaranteed. However, a 6% increase every activation could be cool. At a 9 second cooldown, your cards have a chance of gaining up to (1.06)^10 increase, or 70% with 10 seconds left in the game. I dunno, this might still be kind of underpowered, considering odds would have to be in your favor and the enemy couldn't trounce you with a sabotage. Plus, most games would end before this became effective.
3) It's over. Not much different from a ritual of doom. But with this, the winner would be the guy who started with the lowest hit points. I well-guarded and healed gargoyle would win almost every time. I could see this becoming OP. To be honest, I like how Ritual of Doom operates, especially with how many decks can survive it (though get severely hurt).
4) Blood Seeker. A strong AOE (area attack) card could make this trigger card pretty OP. This might be better the other way around... once your total health drops below 50%... or maybe each time a card dies... this card activates if the cooldown is up. Basically, this puts your deck into berserker mode if your deck starts getting hurt. My suggestion.
5) Greed Pot. I don't see anybody playing this, as it gives your enemy the same advantage it gives yourself. Well, doing some math, you gain some advantage, but not significant. It could add some randomness to it. Why isn't this lootable?
Some card ideas from me (I have no artistic ability, so I'll just throw out the ideas):
1) Trigger card that slows down spells. So if somebody plays a heal card, this would trigger and add 1 to the cooldown. 1st activation = 10 second cooldown. 2nd activation = 11 second cooldown. etc. Maybe have it cap at something like 12-15 seconds.
2) Same thing as #1, just with trigger cards.
3) A spell attack card. It's a spell card, but it attacks other spell cards and either reduces their effectiveness and/or has a chance of destroying the card. You could do the same with attacking trigger cards, or combine this into one card. That could be a pretty lethal legend-level card. Basically, it would reverse the leveling process of the card. A level 40 card hit by this would start acting like a level, oh I dunno, 35 card. Hit again, level 30 card. And so on and so-forth. You'd just need to do math for when the card level goes into the negatives.
4) The opposite of #3, but it would be a trigger card that increases the level of your cards and/or spells and/or trigger cards. Maybe make it hit them all. With a 9 second cooldown, it could increase the level of your cards 10 times. If it goes up 4 levels each time, your card could potentially reach level 80 (in a theoretical way, if the card starts at level 40). So the deck gets stronger the longer you play. The beauty of this card and the one before it is that it only gets effective if the game goes on for a while.
5) Trigger card: A bloody death. When one of your friendly units die, it causes an explosion that damages the enemy by a certain amount. Maybe it's maximum damage, spread between all enemy cards. So if I have a card with maximum damage of 450, when it dies it will do 450 damage to a card if the enemy has 1 card. If two cards, 225 damage each. Actually, now that I look at it, it seems a little underpowered. Okay, maybe it does maximum damage across the board, no matter how many enemies. Or, for leveling purposes, a percentage. Level 1 card would do 90% damage to all the enemy cards (mitigated by armor). Level 2 card would do 91%. Level 10 card would do 99%. Level 20 card would do 109%. Level 40 card would do 129% of max damage to all enemies. Oh, I like this one.
6) Magic booster. I'm surprised this isn't in the deck yet. You've got the melee attack booster, the pierce attack booster, and the fire attack booster... but nothing for that magic/special attack. Where is it?
7) Make something like Duke Vamp and Evil Lich card that applies across the board. So when it activates, 10% of damage performed will be added to all of the card's in his deck. If this card attacks and does 1,000 damage, then each card in the deck will go up 100 damage and 100 hit points. I'd give this a longer cooldown, maybe 11 seconds (9 activations max). An army of these could get REALLY fun.
8) A unit card that slows down on each attack, but the damage goes up. Maybe a 25% increase. So if it attacks at 9 second for 500 damage, the cooldown will change to 10 seconds (unless hit by something that slows it down even more) but the damage will increase to 625 damage. Attack #3 will be 11 seconds after this for 781 damage. This gives it a maximum of 7 hits per game and the last hit would be for 1,907 damage about 80-something seconds into the game, assuming nothing else slows it down like a blizzard, paralyze, or that dragon or something.
9) A damage card much like the twister, but the cooldown changes based on the number of enemy unit cards on the board. So, it does 400 damage with a 7 second cooldown, but a second is added for each additional unit card. If the enemy has 3 unit cards, then it attacks every 9 seconds. 6 unit cards, and it attacks every 13 seconds, each card getting hit for 400. As the enemy units die, this card adjusts. If you are up against 3 units, you start with the 9 second cooldown, but if one of them dies then the cooldown lowers to 8 seconds.
10) A leeching spell card, basically a combination of a meteor and a heal. The spell card hits an enemy and whatever damage is caused will go to heal one of your units. If it hits the enemy for 300 health, one of your cards (weakest? random?) gets healed for 300 health. Leveling this card you can either increase both numbers, or heal for a percentage more. The first option, increase both by 5. 305 damage and 305 heal. Or do the percentage like with that shield, say 1%. So at level 2, you do damage for 300 but you heal for 303. At level 40, that would make damage at 300 with a heal of 417. Hmmm... maybe make that a 2% increase, so at level 40 you damage at 300 but get healed for 534.
11) Ol' Money Bags. Every time this card attacks, the enemy drops some gold, like a % of the damage done. Let's say 5%. If Ol' Money Bags does 300 damage, 15 gold drops. The winner of the match gets the gold that drops. The only bad thing is that this would add a lot more gold to the game, which I think is a good thing. It could mean an extra hundred gold or so could be produced per game, but people would still strategise to WIN that gold. Playing 6 of these cards would probably be so weak they'd lose most of the time with the enemy making some extra cash and not the player. Note: I'm not suggesting that this money gets leached from the enemy, people would get upset if they lose a game and notice their gold is now in the negative.
Well, this is off the top of my head. I have noticed I have a pattern for making stronger cards for end-/late-game fun. I like playing the berserker bears, I think that was my source of inspiration. Plus, I hate games that go 99 seconds long.