- And this is about a unicorn who learns about love and friendship. Perhaps the Unicorn's story becomes the inspiration for future Equestrian society.
- The alicorns are descended from the unicorn who defeated the Red Bull. After all, everyone knows that Red Bull gives you wings.
That is why he is only happy at the sight of them, but he doesn't know why - he forgot about the time long ago.
I know; Schmendrick said that unicorn didn't have any children. But, if he were mistaken about that, then Haggard being descended from a unicorn and a princess links in to his royalty, his dissatisfaction with life, and his love of unicorns.
Haggard seems more of a warrior than a magician, so perhaps the wizard Mabruk taught him to summon the Red Bull, or summoned it himself and bound it magically to Haggard. Mabruk was the cause of all the problems in the story, and gets away with it at the end, because after all, "Nothing ever ends," and there's always another quest to complete or villain to defeat.
- It's what this troper always assumed. Mabruk's presence in the story is completely unnecessary and could have been removed with little to no changes. I think it very likely Beagle invented him purely to make Haggard controlling the Red Bull seem less strange.
- This troper always thought that maybe the Red Bull was a physical manifestation of Haggard's despair. When Schmendrick tells the Unicorn about rumors regarding the Red Bull, one is that the Bull keeps Haggard prisoner in his own castle. What if this is true, but isn't so much literal as figurative: the Red Bull is essentially Haggard's intense depression, made into a terrible creature whose only instinct is to seek out the one thing that makes Haggard happy? People who suffer from depression often feel trapped by it — and for many, it feels worst at night, which is when the Bull comes out from the bowels of Haggard's castle to seek more unicorns. Perhaps Mabruk, being a magician, took Haggard's despair and unhappiness and made a monster out of it.
It would explain the white hair, purple eyes and connection to a mythological creature. They also for some time think they are the last of their families/kin.