No trouble friend.
Its mentioned what? All of three times in the lore total at present? And twice in novels and only one confirmed usage in a game, and then only in a DLC?
I am not surprised folk have forgotten or even never heard of it.
And i agree, but i am of the mind that the blood is merely a component of a greater magical construct, Namely the blood makes locating the target easier, but i have a mind that near anything (Hair, Flesh, etc) could be used from the Donor and it would function in a similar regard. Given Scrying works better with Blood but can still be used with out it, and It is a gray blood magic as well.
I just figure its done for expediency's sake, not outright need of it.
Is Scrying what Finn did in WH? I haven't played the dlc, so I don't recall the name.
In which novels it was mentioned?
We know that blood, in general, is powerful. It gives power, as it's shown even in the GW and Reaver rituals.
I recall that Finn feared that the Chantry might be against what he did, which is the logic behind people saying there is a bi of hypocricy in the Chantry using Phylacteries. They're not blood magic in the sense that are spells empowered by blood, bt the blood is. Still used with magical purposes.
Which might be what Gaider mean with 'blood magic'. The same goes for the Joining, which can be considered a form of BM.
Granted, if you believe that BM is just the empowerment of spells through blood, those above aren't BM, but there are people in Thedas (and in the Chantry/templars) that might consider them BM.