I am wondering if Tsathoggua's ability can be used to kill Tsathoggua. It seems like he isn't very good if anyone that has 5 resources in a domain can just kill him (taking everone else out too, but still).

Also, just to clarify, is it correct that no actions can be played once the struggles begin? I understand that right before and right after you can, but not during.

During struggles you can only play Interruption and Forced Response, no other actions.

For Tsa, if you pay 5 you destroy ALL characters with skill 5 or Lower. So If Tsa has no skill bonus, it will be destroyed like other characters.