Dr. Hooves, as a (blue) Friend in MLP CCG is somewhat of a conundrum.
There are a total of 4 different versions of Dr. Hooves, all of which are either Rare, Ultra Rare, or promo only.
This poses a serious problem when trying to build a deck using Dr. Hooves'.
Dr. Hooves, Experienced Equine and Dr. Hooves, Unblinking can clearly work together, when Unblinking enters the discard pile it can bring out Experienced Equine out in play at Home, (pay 2 to unfrighten him) and move to a problem.
Although both other Dr. Hooves have abilities of their own (they don't particularly work in any real synergy with the first two), they can - once in the discard pile - power up Experienced Equine.
(You could choose to discard other Dr. Hooves Friends with Too Splashy).
In order for a deck like this to function, realistically, you'd need 2-3 copies of each card, and that's difficult considering they're all either Rare, Ultra Rare, or promotional.
This is the mystery of Dr. Hooves. I'm not really sure why he's so difficult to find...