Its actually not terribly difficult to be summoned by the Looking Glass Knight in Dark Souls 2. I researched awhile online and found some people claiming it was hard, but after a bit of experimentation I am now able to be summoned by the Knight every few minutes or so.

Now to be summoned, first and foremost you must be in Drangleic Castle to start out with. Preferrably in the Kings Passage area right before the Looking Glass Knight boss fight. Also note, you can defeat the Looking Glass Knight and still be summoned to other worlds to assist him anyway.

The item you need most is the Red Soapstone sign. To get this you must join the Brothers of Blood Covenant found in Undead Purgatory after defeating The Executioners Chariot. You can only do that by retrieving a Token of Spite from either using a cracked red eye orb to invade and defeat another player or from a chest in The Gutter right after first descending the well and dropping from the bridge on the first wooden platforms you come across.

After you have the Red Soapstone head to the Kings Passage area of the castle. Putting your red soapstone down and repeating this process around every 5 seconds. Waiting doesn't seem to work and only allows other players to summon you into their world. It seems that if there is a "slot" open for the Looking Glass Knight to summon you in and that the window is very short, so keep spamming the red soapstone sign until it reads at the bottom that the Looking Glass Knight is now summoning you. Rinse and Repeat!

Here is a video of me being summoned/ensuing fight!

Skip to around 2 minutes if you wish to see the actual summoning, the first two minutes is me spamming the summon sign like I was explaining.




Let me know if you have any questions! Thanks!