So I was doing some math yesterday for how many sigils would be needed to craft all three Obsidian weapons (thank goodness we keep them after the event is over).
Obsidian Shards are 65 sigils, we need 6 for each weapon, so 18 mats in total, or 1170 sigils
Binding Essences are 135 sigils, we need 4 for each weapon, so 12 mats in total, or 1620 sigils
Perplexing Elements are 270 sigils, we need 2 for each weapon, so 6 mats in total, or 1620 sigils
All in all, one would need 4,410 sigils to craft all three weapons, or 1470 sigils to craft each one.
The mission has 4 depths of random levels, with the second set having 3/5 Plateau, third set having 2/5 Plateau, and fourth set having 5/5 Plateau
My main question is how many sigils can one get on average during the event mission, thus how many times does one need to run the mission?
Here is a relevant wiki article:
http://wiki.spiralknights.com/Lost_Soul#Freed_Soul
On Tier 3 Elite you get four sigils per Lost Soul freed. I'm not sure how many Lost Souls you can expect per Grasping Plateau, and the drop rate changed at some point I think. But maybe a few hundred sigils per level is doable. Someone with more recent knowledge may correct me.
You also get 18 sigils per puzzle solved. Puzzles occasionally also give materials, which are worth many sigils.