Normally, when a GM spends destiny points, it is to make things harder on the PCs: upgrading the difficulty of their attacks or upgrading the ability of attacks targeting them, activating Nemesis features, etc. This flips a point from dark side to light side. Simple.

What about this, though? What if the PCs have NPC allies in the mix - either because it's a feature of the situation/party as a whole or because advantage/triumph allowed for reinforcements - and the GM is controlling them? Of course, there's a secondary debate here about whether or not the GM should control minion groups and other NPCs that are on the players' side (feel free to have that here), but my main question assumes that, for whatever reason, the GM has the reins here. If the GM wants to upgrade the ability of that NPC's attack (because the PCs are in dire straits or it makes sense thematically) or to increase the chances an opponent's shot will miss (if it makes sense that the enemy would shoot at this NPC but they're beloved by the party and you don't want them to die), which destiny point is flipped? Who flips it?

If the burden is on the PCs to say "this NPC is in our camp, and we want to use a DP to help them out", they obviously flip a LS point to DS.

If the burden is on the GM as the controller of the NPC, do they flip a DS point to LS because it's the GM spending the point, or do they flip a LS point because it benefits "the light side"?

My gut says either the PCs have to make decisions about when and what to flip or the GM can choose to flip but it's a LS point and they have to get player permission, but I want to see what other GMs think.

Light side destiny points are a player resource and should be treated as such. If they want to improve the NPC's chances, they can. Otherwise, the NPC is on their own. NPCs generally aren't fated enough to warrant that sort of thing anyway, and those who are probably have other types of resources to call on.

In my experience a player shouldn't spend LS to increase an NPCs roll - not saying you/they shouldn't - rather spend excess advantage to give the NPC an advantage die or two for their next roll.

I had this same problem when the system was new. In the end, I ruled that the players still flip LS token to aid an ally. If they GM wants to do it on the players' behalf, they still use dark side. However, it's better to just ask the players if they want to upgrade the NPC's check and have them spend their resources to do so.

If the destiny point is assisting the side of the players, it should be a light side destiny that is used, so it's up to the players to use on an NPC ally. Generally, it's best to save your destiny points for yourself and not an NPC.

The GM flipping LS DPs to 'aid' the PCs sure sounds like a real source of potential abuse by the GM. I'd stick to the GM controls the opponents, and PCs control themselves and allies.

In one session I experimented with the idea of letting PCs flip dark side points to increase the difficulty of their own rolls. Worked great at first, but was quickly abused as the players learned to strategically use all the dark side points on meaningless easy rolls.

The system works best when PCs flip light side points for their benefit. If they have an ally NPC and the PCs want to flip a light side point to boost a roll from the NPC, I don't see any reason why they shouldn't. GMs should avoid making this kind of assist themselves as it will ruin any sense of danger in intense situations. Your players will expect you to bail them out when things get rough. Light side points are their resource to use in these instances themselves. If they are forgetting that they have them, flip a dark side point on an attack roll against them to remind them

Good thoughts, all.

The situation in question came up in what could have very easily been an extremely tough fight for the PCs (three groups of four stormies, an additional group of two with a light repeating blaster, and Balrekk the Butcher - a Nemesis that's basically a Stormtrooper Sgt. without Adversary but better at shooting and nasty crits); they elected, on a lot of threat from an attack against them, to have them grant "the enemy [the PCs] a significant advantage", which we decided would attract other Rebels involved in another firefight. I ended up in control of the NPCs as it was easier given the situation and format of play-by-post.

Later in the fight, when things could have really gone south and the PCs had no Destiny Points on their side, I toyed with the idea of flipping two DP on the NPC allies' attack - one for the ability and one for the difficulty - just to give the PCs some to actually play with. Then I realized I had no idea how the situation worked. It was then that I realized I would probably have to flip a Light Side point as the GM, which just felt wrong to me... after all, as people have pointed out, those are supposed to be a player resource, and it's extremely abusive for the GM to waste them on NPCs.

So I thought I'd see how people thought about handling that moment here. Thanks for sharing!

Dark side points generally shouldn't be used to upgrade an ally's attack, but using one to upgrade the difficulty of the attack is perfectly valid. While only a single DP per attack is allowed, there's no reason you can't do this with multiple attacks. If you end up doing it with every ally's shot that just goes to thematically show that the PCs are the Big Deal here since the dark side's influence isn't hobbling them like it is the mooks.