It takes 150 Blood to summon Lok. After the Primalist heads to the center of the field, you need 10 people to protect and help summon. Its not that hard to do if people are actually turning in blood.

We were able to summon this with ease a couple hours ago. Here's how you do it:

Loot the blood from alliance corpses (I'm reading 150, but I'm pretty sure it's more like 250, which breaks down to maybe 10-15 corpses). Spam right-click on Primalist Thurloga; which automatically turns in 5 at a time. Once she's activated, it becomes a bit like an escort quest. Her and her 3 npc escorts actually do some pretty decent damage along the way too.

She will work her way to the west side of the field of strife to start the summoning ritual. When she starts the ritual, 10 players have to click to help her summon Lokholar. Only click once. I believe clicking on it multiple times may reset the timer. He starts out kinda small and weak, gaining power with each killing blow he does. You can also buff and heal him. After just a few kills, he becomes ENORMOUS and starts 1 or 2-shotting everything is his path. As this point, you will be laughing your ass off. Don't forget to alt-z before filling your hard drive with screenshots! xD

Also...Lok will wonder around the center of the map for about 10 minutes before beginning his rampage. You should probably leave a few people to guard him. He's kinda weak at this point.

As long as it's not a total zerg-fest, you should have plenty of time and reinforcements to pull this off. glta :) Long live classic AV!