Dark Candy Tree (DCT) was added in Beta 30.0. Previous Versions can be found here.
DCT is a strong, litteral supportive monster with the ability to restore 2 HP to any attacking monster on your board (aside from itself), somewhat providing them with Knight Knight's passive effect (though healing before the attack rather than after).
Very useful in Kindness decks and alongside monsters that have an ability that requires them to be damaged, like Receptionist 1, MTT Fountain or Mirror. The latter two also help protect it from attacks due to their Taunt. All three also work very well in Kindness, being able to increase their HP using Force of Nature and remove the latter two's Disarmed with Heal.
While it doesn't heal itself, you can work around that by using 2 DCT's, as that lets them heal each other (and heal the 2 remaining monsters double as much). Since Beta 48.0, this is even expanded, as any of your attacking Plants receive a +1 ATK bonus on top of their +2 HP healing. And since DCT is one itself, this applies to two of them buffing each other as well.