How do you differentiate them? Is something that's “bad” (lose life, discard, pay mana, etc.) always detrimental? Same for non-detrimental? What about the board state, for example a triggered ability that draws a card while you have no cards left in your library?

Can someone helps me/give me a link where the clear line between those is?

Thanks!

For me, I read the ability and ask myself “would this ability make me want to play the card more or less?”

For example -

Dark Confidant: Without the ability, it's just a 2/1 for 2, which I will be much less likely to play than if it had the ability.

Emrakul: Without the shuffling ability, it's easier to bring it back from graveyard, so I consider it generally detrimental.

It's not 100% perfect, but it usually works for me.

As a good start for getting a sense of these things, you can check out the Missed Trigger Guides on the Judge Wiki.

Note: there is a link at the bottom of the page that goes to older sets as well, though it still only goes back to M13 / Innistrad Block.

Although the distinction is fuzzy in general, there are a few that are easy to classify:

- ‘May’ triggers are always non-detrimental. The controller of the trigger could chose not to do the effect if it worked against them, so there is never a downside.
- Triggers your opponents make a choice about (e.g. Desecration Demon) are nearly always detrimental, for mirroring reasons.

I've found poking through old forum posts about this is a good way of building up some intuition on this front. Many of these threads aren't so cut and dry with the answer, but the responses can be enlightening.

Edited Talia Parkinson (March 24, 2014 12:05:29 AM)

Edit: Aric beat me to the link! Great answer too.

If you're interested in recent sets (especially Standard and limited formats for the current set), Abe Corson leads a project for identifying which triggers are detrimental or not.

Here's the link for the Judge Wiki:
Missed Trigger Guides

You can pull some general ideas of what's considerably always bad and what triggers are in place to make the card more or less aggressively costed. Desecration Demon is a 6/6 flyer for 4 mana. That trigger has to be detrimental.

Generally, do NOT look at board state. Think more about the intent of the card and its design to determine if the card is generally detrimental. If the board state makes something considered non-detrimental not a good thing (like a draw trigger when the library is empty), you can consider that for an investigation to determine if the player is missing their trigger on purpose.

Edited Evan Cherry (March 24, 2014 12:09:27 AM)

One important think that I know threw me for a loop is that, although you are not supposed to consider the board state, you can consider whose turn it is! (ex. Sulphuric Vortex is detrimental on your turn, and beneficial on your opponent's turn)