1. You can invoke an aspect you created (such as setting a dude ON FIRE, and then getting a +2 on your attempt to hit him with your gun because he's too busy being ON FIRE to dodge), or you can COMPEL the aspect on him, to, say, make him miss the dodge entirely (no roll). The difference is, if you compel it, you pay a fate point (or the GM lets you do this with your free tag, which i've heard varying responses on this), and the bad guy has to accept the compel and GAIN that fate point, or refuse it and PAY a fate point to the GM. (you still lose yours). So you're choosing to take a decent gain (a +2), or to get a possibly bigger gain (auto-fail on the NPC action) in exchange for a fate point.
2. I'm not really sure. Mechanically, they do the same thing.
3. The creature is blinded. The player can compel that behavior, but so can the GM. Usually, you'll want to hit this with a good compel, like, shooting the creature and compelling that to cause him to not be able to defend. Instead of a +2, you'll pretty much treat him as if he failed an alertness roll (indeed, if your GM is arguing this, you should simply stealth, compel the alertness roll, then fire)... so he'd be at 0 defense, and then wouldn't get to roll. But, the next round, when he's still blinded, you're going to need more fate points to keep that up. Sometimes, a generous GM may compel it for you... but regardless, because the creature took the first compel, he now definitely has a fate point to buy out of the second one. Still, it can wreak havoc on an enemy quickly.
I'm trying to put together a summary sheet for aspect-related terminology for folks who have either never played a fate system game, or whose fate experience has been largely with SotC (this includes me). In doing this, I've uncovered all sorts of things I don't myself know/understand about the basics and finer points. I've got a few questions that I'd like to propose to the board to see if I can get a better understanding of certain elements. I'm also including a link to the google doc with the summary sheet as a work-in-process. If anyone has any corrections/criticism, I'd love to hear it.
Link: http://tinyurl.com/2crr6sy
Here are the questions than I have outstanding after looking through various threads here (the Igor/Voldemort fight example, and resultant discussion were very informative).
1. Can you tag a newly created/discovered aspect on a hostile NPC for a compel, or are tags strictly limited to invokes?
2. What’s the difference between a compel on a hostile NPC’s aspect, and an “invoke for effect” on a hostile NPC’s aspect? Is it that that you can "invoke for effect" only when the result is not directly detrimental to the NPC in question?
3. I'm still a little confused on what effects aspects created by a spell have. Since this example has been used elsewhere, I'll mine it again: Harry Blinds the Loup-Garou. This spell applies the aspect "blinded" to the target. I assume this aspect can be mined in all the usual ways: tagged for a free invoke (e.g. gain a +2 on a stealth roll against the target), compelled (e.g. "the blinded Loup-Garou is lured through the open door of the cage-trap"). Narratively, the Loup-Garou is blinded, but how is there ever any persistent mechanical effect of this aspect that doesn't require the investment of fate points?
Any input is greatly appreciated. Thanks in advance!
-Scott