Well, dang. Helheim just broke their NAP3 in order to launch a surprise attack against the noble Argathan people. Which I wouldn't mind so much, except that at one point or another *every* single neighbor of Argatha, with the sole exception of Caelum, has decided that it would be a great idea to attack us. Of course, they have all regretted their decision in time, after facing our fierce armies and ingenious strategies. Soon Helheim will feel the same regrets. But in the meantime, if anyone wants to take some of Helheim's land while their attention and armies are elsewhere, feel free.
And don't let any pesky treaties you have with Helheim stop you. Those treaties will not stop Helheim from using stealth and cloud trapeze to launch a massive surprise attack on you when the time comes.