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Terrain cards come in two main categories. There are 'world' cards which come into play and remain in play unless removed (rather than a one-use card), which typically alter something about the general world. Multiple of these can be active at a time, though any that would contradict have both effects nullified. The second type are cards that, similar to the Expedition cards, placed in lanes face-down behind one's Pokémon and activate in response to attacks. All of the Traps in the regular Pokémon Mystery Dungeon games would go in this category.
You can place Pokémon, Terrain, and Expedition cards face-down, and only pay for their Supplies when flipped. Conversely, if you place down a Pokémon without being able to give it the correct Supplies once it is flipped over by an attack or card effect, that Pokémon is instantly K.O.'d.
Things such as status effects would also exist, though would be different than the TCG variants. Burn would cut all attacks in half for the specified number of turns; paralysis would allow the Pokémon to attack/move only every other turn; freeze would stop Pokémon from moving; sleep would prevent Pokémon from attacking OR moving; poison would do 20% total HP damage rounded down each turn. Conditional status effects would come up as explained on the card, but the purpose is to remove as much "flip a coin" stuff as possible.
So, to sum it up, this game would focus on positioning and resource use with a heavier bearing on strategy and skill than luck.
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