Heresy is a tricky concept to implement. I will break it down because I am aware that my thought processes and intentions may not be clear from this card alone.

Heresy will always involve the creature tapping to activate an ability that will generally have negative consequences for the creature's controller. When that ability is activated, the creature has committed Heresy, and the second ability will trigger.

Each Heresy is not the same. A blue creature may have its controller mill three cards as Heresy or a red creature's Heresy may deal damage to a creature the player controllers. I cannot figure out any Heresy abilities for white that seem logical (and green's seem like forced bends). This worries me that Heresy would not be viable. As a. note, I should mention the other mechanics intended for this set do restrict themselves by color. While I considered making a unique mechanic for each of the five cults, that would be too many mechanics for the set, as the set needs mechanics for the theme of color identity.

This card also grants its controller the trigger from committing Heresy when a similar act occurs. This was added onto this card to just be more versatile in general. While not every card would have a similar clause, it likely would not be hard to include (e.g. the aforementioned red example having "Whenever a or creature you control deals damage to a creature you control or you commit Heresy, do X thing.)

I wonder how much easier the concept was to grokk if the activated ability line read just ": You lose 2 life. Commit heresy."

The current wording implies that the nature of the activated ability is changed.

Here a note though about something that I consider definitely not intuitive design:

> "When that ability is activated, the creature has committed Heresy, and the second ability will trigger."

So one trigger condition is on life loss (happens during resolution of the spell), but the other is on activating an ability. In consequence condition will cause the ability to enter the stack after the spell/ability has finished resolving and the other will trigger with the spell/ability still on the stack and no life lost.

A benefit of putting "commit heresy" straight into the activated ability's effect would be a more consistent timing.

"Heresy" sounds like the effect should be something violating/threatening the color's beliefs. I don't know the other cult abilities, but maybe you could play on them; I'll just play on abilities that technically any color can use (as a cost, usually), but usually don't, but that directly tax a resource the color usually wants to have around e. g.

• white life-loss
• blue discard
• black exiling cards from graveyard
• red scry
• green creature-sacrifice

I'd expect that to feel more like heresy from within the mechanical default frame of thinking MtG provides.

Saying Commit heresy after the activated ability works for me if you think it helps. I think this suggestion solves your second issue as well.

I was thinking Heresy as something the color would due to another player but instead doing to itself. Doing the opposite of the color is interesting, and I'm interested to see how this is. Oddly, I was likely to use creature sacrifice for green, as it's something green does, but usually to reap something benefit (drawing cards or putting out another creature).

With this particular card, I'd worry that people will think the life loss from the first line will trigger the second line. As currently written, it won't, because a creature on the battlefield is not a spell, but a bunch of players won't realise that. (I'm not 100% sure whether you intended the lifeloss from the first line to trigger the second line.) I'd suggest changing one or the other so they're not so confusingly parallel.

That's fair. It's clear to me, but I've seen players get tripped up by Haunt.

I don't think I'd remove the spell trigger, but maybe writing "commit heresy" first and then "or a spell causes..." after might make things more clear, especially with SecretInfiltrator's suggestion wording structure having "Heresy" be the name of the ability.