The blood diamond causes crash.
Crash Log: https://pastebin.com/TWZAWdxy

Blood Arsenal: 2.0.1-14
Minecraft Version: 1.10.2
Forge Version: 12.18.3.2254
FML: 8.0.99.99

Edit:
The blood diamond seems to have caused the world to not load.
Here is the log

When does this happen? (or how does it happen)

I should've specified.. whoops.

The crash happens when you're crafting the blood diamond it's self. Multiplayer servers are safe because of the rollback that comes with a crash but singleplayer worlds seem to just, crash.

Confirmed and testing, seems to actually be a Blood Magic bug but will report back with more details.

I recently also experienced this issue on our multiplayer server with the same crash report. Was wondering if there have been any updates on this bug.

@heyoomimi it's an issue with blood magic, so if you want to make a post on /WayofTime/BloodMagic/ outlining what's happening I'd be greatful as I'm not currently at my desktop.

Fixed in the latest version due to me changing the recipe, although I should really go fix this on Blood Magic's side as well.