User blog comment:B214/Question and Answers 6/@comment-217.115.65.19-20190123111025/@comment-10330822-20190125024458

Here's the deal. Unlike Twilight Healing, Forbidden Balor View has a piece of the Evil Irish God Balor inside of it. So unlike a sacred gear with a special function, the Forbidden Balor View is indeed one of a kind and unique, because there is only one Balor.

They mentioned very early on that individuals powers can mix with the gear and turn them into something much stronger. This causes special manifestations of Sacred Gears to appear.

In Gasper's case, his unique vampire origins mixed with the gear to turn it into Aeon Balor. Just like how Ingvild's natural water control and music talent enhanced the attributes of Nereid Kyrie.

The problem in the series is that even the non-rare Sacred Gears only appear once or twice. So the rarity of the situation of something like Twilight Healing is lost on us.