Tzeentch is the Warhammer Chaos God of Magic. "Tzeentch's Curse" in Warhammer Fantasy Roleplay (2nd edition) is how that game implements the risks of (arcane) spellcasting - there are no mana or fatigue points in WFRP, so Tzeentch's Curse is what's supposed to hold a wizard back from solving every problem by casting magic at it.
In summary, it manifests as a small risk of every spellcasting that something bad, strange or spooky happens (regardless of whether the spell succeeds or not). This could affect the spellcaster directly, but its most important impact is indirect - these curse effects can reveal a character as being a spellcaster, and if clearly supernatural effects are happening... well, in the Warhammer world superstitious and uneducated peasants and rabble are known to take matters in their own hands, by hunting down and burning "witches" and "chaos sorcerers".
Now, Dragon Age appears to be more open about magic, so this aspect of Tzeentch Curse is probably not wholly appropriate for this game. Instead, it seems to be more a matter of corruption - somewhat like how you get nasty side-effects from casting dark magic in WFRP or how your Corruption score in Dark Heresy increases with exposure to the Warp. Mental breakdown and physical mutation, in other words.
I'm sure this is something we will learn more about in coming box sets. In the meanwhile...
Because Dragon Age generally
wants you to roll doubles, I'd use a different triggering mechanic for curse/corruption effects.
Perhaps if you roll a series? Like 1, 2, 3 or 3, 4, 5...? The Dragon Die would still be the important one, indicating the severity of the curse/corruption effect:
Dragon Die shows '1' (a roll of 321): ...
Dragon Die shows '2' (a roll of 432): ...
Dragon Die shows '3' (a roll of 123 or 543): ...
Dragon Die shows '4' (a roll of 234 or 654): ...
Dragon Die shows '5' (a roll of 345): ...
Dragon Die shows '6' (a roll of 456): ...
Fill in Catastrophic Manifestations or Profane Corruption as you please
