
Zhayne |

I'm 99% sure I'm right on this, but someone in our group isn't, for reasons to be detailed below.
Player A encounters a monster. Player B has two blessings in his hand and an ally that lets you give a card to another player.
Player B wants to play that ally and pass a blessing to player A, so that he and player B can both play a blessing on the Check To Defeat.
I'm certain this isn't legal, because it doesn't directly affect the Check To Defeat. Apparently, though, the PACG mobile game (or whatever it is) *does* permit such a maneuver, which is why he thinks it is legal.
So, final answer ... ?

skizzerz |

It is not legal.
In some situations, you are limited to playing cards or using powers that affect or otherwise relate to the current situation. In these cases, the things you do cannot require anyone to do something else for your action to be meaningful—the things you do must directly affect the situation. For example, let’s say that a character is attempting a check using a power that adds 1 to her check for each blessing in her hand, and a second character has a power that allows him to give the first character a card. He could give her a blessing, because that doesn’t require any other action to affect the check. But he could not give her a card that allows her to draw a blessing from the box, because she would have to do something else—in this case, play the card he gave her—to affect the check.
In the example, passing a blessing is only legal because there was a power which affected the check that counted the number of blessings in hand. If that power was not in effect, it would require another action (playing the passed blessing) to have an effect.

skizzerz |

Gotcha.
There are days I question whether or not the ACG is actually less complicated than the RPG. ;)
Something something Sacred Geometry (ok that feat is just downright terrible, but there are a number of things in the CRB even that have far more nuance than the ACG can even dream of approaching. Simulacrum springs to mind as another nightmare to puzzle out, as is light and darkness. For something more mundane, check out combat math at higher level play when you have buffs/modifiers from over a dozen different things, some of which stack and some which don't stack and only the higher between them is applied. The ACG is far, far simpler)

Yewstance |

This is something that has confused me greatly before. The best example that baffled me was the Manual of War and how it interacted with power feats.
I could understand that I could get into a check that uses, say, Strength, and then use Manual of War to give myself a +1 Strength Skill Feat. But could I use it to give myself a new power feat which would THEN have to separately be used in order to effect the check?
For argument's sake, if you can check a power feat to get the text "You may discard a card to add 1d8 to your Strength check"... can you get into a check, then display Manual of War to check that feat, and then discard a card to use the power feat? Is that 'directly affecting the check'? How is that different from "I'm giving you a card with this effect, and that card I'm giving you will optionally affect the check", just in this case its "I'm using this card to get a power, and that power I'm getting will be able to optionally affect the check".
Note that, as Hawkmoon pointed out to me, these rules were clarified in Mummy's Mask, and as per the FAQ:
Rules: Affecting the Situation
In some situations, you are limited to playing cards or using powers that affect or otherwise relate to the current situation. In these cases, the things you do cannot require anyone to do something else for your action to be meaningful—the things you do must directly affect the situation. For example, let's say that a character is attempting a check using a power that adds 1 to her check for each blessing in her hand, and a second character has a power that allows him to give the first character a card. He could give her a blessing, because that doesn't require any other action to affect the check. But he could not give her a card that allows her to draw a blessing from the box, because she would have to do something else—in this case, play the card he gave her—to affect the check.
This, incidentally, also answers OP's question - if you had an effect that changed in power depending on how many blessings were in your hand, you COULD have an ally pass you a blessing. Presumably, there's nothing stopping you from using that blessing then, as well. If you don't have any such effect, it's an illegal move (which seems... odd, in some ways. That potentially gives some effects an almost invisible, but meaningful, 'buff' by suddenly making some forms of teammate assistance legal).
P.S. Skizzerz later agreed that, rules-as-written, it's probably not allowed to use Manual of War to gain a power which would THEN require an explicit action before affecting the check...
Some powers are "always on" such as a power "Add 2 to your checks to defeat Barriers." You could Manual of War such a power during a check to defeat a barrier. With that sidebar, I believe that you are correct in that gaining a power that would then require you to use it is not allowed. However, that card was made before the sidebar was, and I believe that the intent is to grab any power that would then be relevant for the check at hand. As such, at my table, I would allow you to gain any power as long as you then use that power.
...but this supports my assertion that "What is/isn't immediately relevant to the check at hand" seems to be somewhat debatable, and the design intent may have even changed over time. Either way, probably best to agree on something on your group, and stick to it.

zeroth_hour2 |

This is because the ruling was reversed with the Affecting the Situation sidebar, mainly because of the number of nests you could get into if it could chain like that (like Rage).
Rage was created before the sidebar and was errata'd to specifically allow you to play it during a check to get around the sidebar. Manual of War does not do that, so it was intended not to allow you to get around it.

Yewstance |

This is because the ruling was reversed with the Affecting the Situation sidebar, mainly because of the number of nests you could get into if it could chain like that (like Rage).
With all due respect, I already quoted the relevant passage. The last post by Vic in the threat you linked is the same FAQ that I quoted in my post.
Perhaps I didn't make it clear that I am familiar that this is an issue that has gone through multiple rulings and changes. When I said that design intent MAY have changed in time, I was largely referring to the possibility that certain cards and characters were designed for a rules environment that has since changed and rebalanced them. Rage was a significant case, hence its explicit errata, but I wonder if there are other cards often swept under the rug that don't match the original intent.
But, as stated, rules-as-written is unkind to many uses of Manual of War, unless you're utilizing it in advance of running into checks.