Default summoning cost

I agree with Yamahako in paying for the total costs when the cards are revealed. A further step that you can take is that a player must pay at least 2 chips for each monster played, but are able pay more (the chips paid can simply be placed on top of the card). This will allow players to bluff by overpaying for weaker monsters or underpaying for stronger monsters.

Well those other aspects of the game weren't explained in the original post...

I don't know how calling and raising work in this context.

Does the opponent raise or call by playing monsters of his own? Or is he betting against the success or failure of your monsters against a random threat? Need more information to help better on this I think.

It could still work. It would work even well for bluffing (in favor of the bluffer).

The question is whether or not all Dragons are the same (let's assume they aren't)

I have 2 (1) cost Dragons, and 3 (2) cost dragons, and 1 (3) cost dragon.

I play 4 cards down, and my 8 chips. I played 2 (1) cost Dragons, and 1 (3) cost Dragon) and 1 (2) cost Dragon.

My opponent Raises me by 1 (playing 5 unicorns), so now he has 10 chips in the pot, and I have 8.

I Re-raise by playing my other 2 (2) cost dragons, leaving me with 12 chips in the pot.

My opponent plays another dragon to call me.

If either of us were to fold, the cards wouldn't be revealed and the last person in get the whole pot (with no cost reductions), and I would have underpaid for higher cost dragons, and overpaid for lower cost dragons. But we didn't.

My opponent had 1 (1) cost Unicorn, and 3 (2) cost Unicorns, and 2 (3) cost Unicorns. He has to put in 1 more chip [2 (3) costs, but 1 (1) cost, nets to +1] {If he couldn't pay he would have to discard one of the 3 cost Dragons}. I remove 1 chip from the pot, since I'm over invested. Leaving a 2 chip spread. Let's assume that his higher cost dragons are more powerful than mine, he then wins the pot.

If I want to bluff, I can play a lot of lower cost dragons to try and scare someone away from investing. Or if I want to downplay a strong hand, I can keep calling with powerful dragons (that I will have to invest extra money into the pot).

I don't know that its a perfect system, however I think it has enough interesting decision trees to be worth testing - if what you really want is a hidden variable cost mechanic.

Ahh ok I understand now.

So say there are 3 types of creatures. Dragon which costs 3, Unicorn which costs 2, and Squirrel which costs 1.

If I understand correctly, I play a card - and then pay 2 chips per "copy" of that creature I'm committing to the battle. This makes me the aggressor. I'm assuming being the "aggressor" changes the battle formula in some way - though if it doesn't that's fine.

My opponent then plays a card (might be the same, might be different, these are face down so we don't know), and then pays 2 chips per "copy" of that creature as well. If he out pays me for creatures then he becomes the "aggressor". Right?

Ok so how you could do a variable cost mechanic for that. When you play the original card face down, you put chips on it. These chips pay for the monster - but not the copies. You can over (but not under) pay for the monster. Maybe make it so you have to put 1 chip on the monster, but can pay up to 'X' chips. This means you can bluff a cost 1 monster is a cost 3 monster. These chips are lost to the pot if you fold similar to ante in a poker game. Additional monsters still all cost 2 chips (the extra cost would be absorbed in the initial card play). You could then balance out that first card - really powerful card might cost 5, really weak ones might cost 1, and then 2 per monster you summon.

Would that work?

Yup that's kind of what I was suggesting. You would want to overpay to bluff. You never want to bet up a weaker hand unless it's to bluff. I don't know how the calculations run to determine the winner - if it's a strictly "my number is bigger, I win" then you're right this won't be that simple. But if there's some interactivity in which monsters beat other monsters - then the bluffing mechanic could be interesting (overpaying for a weaker creature to get the opponent to fold or whatever).