Cards with the rarity 'Determination', reserved for characters strongly linked with Determination. These are the hardest cards to get typically received by expert players (LV 40+) who reach Diamond or Master in Ranked, as those ranks award the player with "DT Fragments". These fragments need to be used to craft DT cards instead of Dust. (You also receive Frags by selling DT's.) You need 2 Fragments to craft one. However, you can't choose the DT you want. When crafting a DT, you instead get a random DT monster you don't own yet. Once you have one of each, crafting another DT will give you a shiny version instead. These will also be given randomly and check if you already have a shiny version of it. They also cost 4 DT Fragments instead of 2.
Final Packs are also another way to obtain DT cards, but the only way to get one (as of Beta 10.3) is by reaching level 200. Final Packs, like Super Packs, give one of every rarity. But instead of a Common, a Final Pack gives a DT instead. (So it gives a Rare, Epic, Legendary and DT.)
DT cards are represented by the red colour heart on the bottom centre of a card. A special ability of DT monsters (which is listed on some of them) is that they are immune to Silence. This ability is actually in the coding of the card itself and not an actual ability. As such, any new DT monster will also be immune to Silence, while all other rarity monsters can never have it.