Utilizing a "Mini" Deck of 35 cards

Here are some options to consider:
- Allow player engines to do things besides combat abilities: earn victory points, add to life total, increase the number of attacks on future rounds, increase allowance of cards played on future rounds, etc.
- Penalize a player for having too many cards in hand
- Offer a bonus to life or other resources for playing 2 or more cards at a time (and not a "+1 per card played" bonus, because people will still hang on to cards until they can play several at once)
- Player hands need to stay the same size as the Dealer (if there's such a role in the game, or maybe you manufacture the role), or the player with more cards in hand suffers a penalty
- The player who plays more cards by the end of a given round earns a bonus, or the player who has played less earns a penalty
- Some factor independent of the players determines the number of cards they must play and/or have remaining in hand to earn a bonus or avoid a penalty
- Players start with a small amount of life points, and can add to them with cards played/banked on their turn. No more cards can be added to life points as soon as one player has launched an attack against the other.

Hopefully something in there might be worth keeping. :)

Ideas for limiting number of cards in hand:

Why would a player want to hoard their cards instead of playing them to develop their engine? What ever the answer to that question is, if you can reduce or eliminate it I think you on the way to finding a solution for this concern.

Could you limit the number of cards played each turn? I know that this seems counter-intuitive, however if you place a limit on the number of cards played, players will try to make sure that always play that number of cards.

You could also allow a card to be placed down for some sort of default reward/action. This may also help in eliminating the discard pile.

Idea for elimination of discard pile:

Eliminate one shot cards or pair them with a permanent effect.

Ideas for encouraging/timing attack

Can you design the engine in such away that that after awhile there is a point of diminishing returns for each engine? This way when players begin reach that point they would start attacking the other player.

Could try to break things down into a build engine oriented deck and a attack the deck? There are numerous possible options from here. You could have to go through the build engine deck then the attack deck. You could have players draw a card from both each turn. You could let the players draw 2 cards and they get to choose from which deck(s).

Good luck. Feel free to disregard, use or improve upon these ideas.