Flatten is a mechanic that was released with set Bit Depth. It decreases the dimensions of opposing Digimon until they shrink into a point and vanish! On its own, flat doesn’t do any damage or cause any immediate effects—instead, it’s a ticking time bomb. So here are the rules:
- When you meet your condition (in the pic, opponent used Circle, or opponent’s type is Dragon), you will cause a “flat” to the opponent
- On attack abilities, only one condition can be met per hit. (If a Dragon uses Circle, it only causes 1 flat, not 2.)
- Track “flat” by taking a card from the top of your deck, if any, and placing it face-down in front of your active. Neither player may look at it.
- If you would ever have 3 flats, you get KOd! Shuffle all flat trackers back into the deck. Note, this means you must have 3 remaining cards in your deck to be KO’d by “flat”.
- If you would take damage while you have the 1st Attack and 2 flats, you get KO’d!
- When you evolve, you can pay 10 DP from anywhere (such as your DP zone or your Immortalize card) to remove 1 flat marker (shuffle it in). You can only remove 1 flat per evolution.
And that’s how it works. Check the rules for an official explanation (glossary or attack abilities). Flatten is specifically intended as an alternate win method, similar to trashing an opponent’s deck out (which may reduce your required KOs). You will still have to use all your cunning and experience to make the most of it, but it can be a powerful KO method. Since it “poisons” a Digimon, opponents may have to slow down their evolutions. Or you could exploit them after they evolve to Mega for 2 KOs. Repeatedly gaining 3 flats can be difficult, even if you maximize your opportunities, so be sure to have a backup plan.