Every depth has a chance to have a Black Hole in it.
Animation is like vortexes, but little bit bigger and black, also it tighten inside like vortexes do.
It will appear suddenly and move all party to another random gate, but same tier and depth. (except Basil and Subtowns)
Black Holes can't appear in depths related with bosses.
Also Black Holes after T3 Basil has a slight chance to get players in the Shadow Lairs.
When it appear nobody can join the party.
Black Holes appear for a random duration, similar to the gate cycles.
If one or more party members was far away from team when it has been moved by Black Hole, he just need to jump in to it too, and he will join his team.
Whatever, because the Black Holes are gonna be big, Knights will not always have a chance to avoid it.
This suggestion should bring more fun in game, and also it will give everyone a chance to explore the Shadow Lairs.
Cheers.
It'd be hard to balance something that lets you get a shadow lair at random for free. It certainly would be in character for the mysterious shadow that causes the shadow lairs though.
I think what shadow lairs need the most is gear that an endgame player would actually want to use, as it stands now all shadow lair gear is good for is bragging rights. =\