Source: Eberron - Rising from the Last War

Prerequisite: No other dragonmark

You have manifested an aberrant dragonmark. Determine its appearance and the flaw associated with it. You gain the following benefits:

  • Increase your Constitution score by 1, to a maximum of 20.
  • You learn a cantrip of your choice from the Sorcerer spell list. In addition, choose a 1st-level spell from the sorcerer spell list. You learn that spell and can cast it through your mark. Once you cast it, you must finish a short or long rest before you can cast it again through the mark. Constitution is your spellcasting ability for these spells.
  • When you cast the 1st-level spell through your mark, you can expend one of your Hit Dice and roll it. If you roll an even number, you gain a number of temporary hit points equal to the number rolled. If you roll an odd number, one random creature within 30 feet of you (not including you) takes force damage equal to the number rolled. If no other creatures are in range, you take the damage.

You also develop a random flaw from the Aberrant Dragonmark Flaws table.

Aberrant Dragonmark Flaws

d8 header
1 Your mark is a source of constant physical pain.
2 Your mark whispers to you. Its meaning can be unclear.
3 When you're stressed, the mark hisses audibly.
4 The skin around the mark is burned, scaly, or withered.
5 Animals are uneasy around you.
6 You have a mood swing any time you use your mark.
7 Your looks change slightly whenever you use the mark.
8 You have horrific nightmares after you use your mark.

Option: Greater Aberrant Powers

At the DM's option, a character who has the Aberrant Dragonmark feat has a chance of manifesting greater power. Upon reaching 10th level, such a character has a 10 percent chance of gaining an Epic Boon from among the options in chapter 7 of the Dungeon Master's Guide. If the character fails to gain a boon, they have a 10 percent chance the next time they gain a level.

If the character gains a boon, the DM chooses it or determines it randomly. The character also permanently loses one of their Hit Dice, and their hit point maximum is reduced by an amount equal to a roll of that die plus their Constitution modifier (minimum reduction of 1). This reduction can't be reversed by any means.