where to place attack and play cost information on a card?

Key information in the top left corner, if people are holding cards in their hand. If the game is mostly about layout, then I'd say clear, bold print in either the top quarter, bottom quarter, or both.

Just take any deck of cards and hold a fan of 7 (or however many) in your hand, and you'll see that the top left corner is pretty much the only thing you can see easily. In particular, what a card costs is "key". Its general type (attack, defense, whatever) is probably also key, though maybe can be relayed through background color, border color, or similar, if not by an icon.

Here are sample "template" cards from "Monster Keep" (MK):

So the first thing you notice AT the VERY TOP LEFT corner, I have the "Attack-Type". So as Jay103 was saying, TOP LEFT is usually your most important information.

In my case this determines which Monster can attack which OTHER Monster according to a simple RPS-3: Melee -> Ranged -> Flying -> Melee.

Therefore, in my own way, the RPS-3 rules determine who can attack who... So even before there are any STATS, you need to figure out WHO will be attacking. Simple enough, no?!

Next I am opting for sliders and the Power & Style stats are on the SIDES of the card (Left = Power, Right = Style).

And then in the bottom area are "Abilities" and on the bottom-most are, I have the CARD NUMBER and a CARD CODE.

Now to compare with your card. I think the TOP-LEFT corner has a TYPE or FACTION association. Is this because the cards are categorized into different "classes" (like Pokemon for example)?!

And then you choose BOTTOM-LEFT for stats. Hmm... This is a bit "questionable". WHY? Because when you "Fan your hand" you won't see this information. My suggestion: Move it to the LEFT-MIDDLE and you will see them BETTER... So you look at CLASS (type or faction) and then check the middle or the stats.

If you want it MORE OBVIOUS, well then I would place the STATS just BELOW the CLASS (type or faction) and they'll probably be MORE visible to aid in choosing to play the RIGHT cards on your turn.

Cheers.

Anything you might conceivably want to use to SORT the cards in your hand should probably be on the top left. In a regular deck of cards you have number and suit and you can see both very easily at all times.

Is there another way to get across the type? Is there a reason you only want one thing in each corner? You could easily put "3 / 2" in a red circle in the top left and boom, you have all three pieces of information there. You can duplicate the 3 and 2 elsewhere (maybe in the middle of the card) if you think people need a reminder of which is play cost and which is attack.

Bottom right is a terrible, terrible choice. Everyone will hate you and tear the cards up in frustration and then burn the pieces.

While I can appreciate the willingness to HELP, that is NOT TRUE! Why??? Because Magic: the Gathering (Magic) has their stats on the BOTTOM RIGHT and nobody is "Crying Foul"! Power and Toughness can be found in the bottom right hand corner of the cards!

So it's not so DRAMATIC or end-of-the-world when placing stats in that corner... True it is the least used spot... But seriously nobody will burn their cards just because a stat is placed in that position (and I state as proof Magic)!

It better be $0.50 Rare! (LOL) I watched Tolarian College Reviews yesterday and now for about $16.00+ USD you can buy ONE (1) Double Masters Booster. That's right: ONE Booster for $16.00+ USD! Now that is freaken expensive... WHY?! Well it's still like $0.05 a card (to make, it's only cardstock). And his point was exactly that: it's only 15 cards made of paper. Same cost to make when they are sold at $4.99 or $16.00+ per booster.

Anyways the whole point he wanted to make is: even if there are TWO (2) Rares per Booster Pack (and it's true, the format states 2 Rare cards per booster) ... most of them are going to be $0.50 Rares...!

So that's where this is coming from: better be a $0.50 Rare ... Cause we all know commons are worth pennies on a dollar. Cheers!

As an example of what I was trying to say. I think @Jay103 has the SAME idea from his posts ... I think he too was suggesting to add more information to the TOP-LEFT Corner... Somewhere lower for the stats...

Just as a reference. The card on the RIGHT is a Gwent card... Again showing you a "similar" layout. These are just some examples. You can design your game according to the style that suits you. I'm just sharing some examples with you!

Note #1: I've just played around with the card... Nothing fantastic... My Graphic Design skills need "a lot of work"! But this is just an example of what can be "improved upon". Cheers!

See those "certain traits" about how the cards perform when combined... That's the "Special Ability" you need to "describe" on the cards. You cannot simply assume that because Pyromaniacs have an "ability" that players are expected to "memorize" (or commit to memory) that "ability".

So in fact, I would argue that INDEED your cards DO HAVE an "ability", one that is related to the cards on the field itself.

You never want to NOT present a certain aspect of the game on the cards especially if it is such an important one...

Sounds to me like a "Special Ability"... Again never commit to memorization, always specify "abilities" on the cards themselves...

My idea would be, in the TOP-LEFT corner is a Power + Faction. The Power is used for Combos, like if two (2) Lil Flame are next to each other and one attack, the opponent's ADJACENT cards would lose 2 HP each (1 + 1 = 2) or something like that...

Again just ideas to work with, expand on, etc. Feel free to use what you like and discard what you don't like.

Note #1: Going with the Pyromaniacs, if let's say a "Fire Lord" was next to Lil Flame and has a "3 Pyro", that means when Lil Flame attacks, ADJACENT cards lose 4 HP (1 + 3 = 4). Something COOL like that...

Note #2: I took the "brain"/intellect out and replaced it with a "coin" which can ONE of two possibilities:

1> The amount required to be payed when putting this card in play.

2> The amount acquired each time this card defeats an opponent.

So it's either a COST or a REWARD. Whatever works best...

Here is an example for a deck building game that I like: Rune Age

https://www.boardgamegeek.com/image/972509/rune-age

Since the purchase cost is not used when the card is in your deck, it has been put at the bottom right of the card. Else, during the game the player will use the top left value which is attack strength in this case.

I think your original idea of putting the COST in the TOP-LEFT corner was more appropriate. And then maybe putting your "Class" or "Faction" in the TOP-RIGHT corner. So this way you can see the cost initially when fanning your hand and then when you have chosen a card you might want to play, you can have a closer look at the "Class"/"Faction"...

In this scenario, you are "focusing" on the TOP-MOST portion of the card to display the stats or information you require rather easily.

There is the notion of "winning the game"?! If one player dominates another that's how the game is meant to unfold. Are you aiming for "stalemates"??? I think you should playtest this A LOT to determine how often does this really happen. If it happens in less than 1/3rd (33.3% or less) then it's not a problem. It's a Game Strategy: flood the opponent with a few STRONG monsters instead of having a bunch of weak ones.

Just something that MAY be of "value" to you:

Why is this important??? It moves the game along and can lead to a quicker victory. Again "Why does this matter?" Because it's a game, you win SOME and you lose SOME. You don't want the games to last FOREVER otherwise BOTH players will grow tired of playing somewhere after the 60 minute mark.