There are some cards that can do you in immediately if you have a Level 3 deck like I do, so I always watch out for them.
For Corn Fields, there is Gold Corn Ronin and Gold Patchy the Pumpkin. Both have attacks over 25, which means if they land on an empty lane, you're dead. Blue Plains has one such card, Gold Psionic Architect, and Useless Swamps has one such card, Gold Tree of Underneath.
For this reason, it's imperative to keep all your lanes filled as much as possible.
Typically, this is how a typical game for me goes:
- Computer goes first, places two creatures down for 1 point each.
- If I have any Black cards, place them on the two empty lanes to immediately hit the computer. If not, place any other 1 point cards with high attack. Even if I have no high attack cards, place cards in empty lanes. Even if the computer already placed cards with higher attack.
- Computer goes again, usually countering the cards I just put down. Also, cards that were placed in the first round get to attack, and may be stronger with a building added.
This way, the computer doesn't have a chance to hit an empty lane, and the computer will never replace an existing creature with another unless that creature was killed off.