While I agree, in a general sense that Immunities aren't fun (run into this with my IST Game at one point and banned them, outright), there is the counterpoint: Not every character will be effective against every enemy.
Also, the Blue Demon, while sentient, is far from sapient. GURPS makes the distinction that many people and games don't. You have to have an IQ of 6+ to be sapient (Character, box, pg 23), and the Blue Demon only has an IQ 4. It isn't sapient. Sure, it can feel pain and has emotions (usually in the "RAWR! CRUSH! KILL! DESTROY! TORTURE!" area), but it isn't sapient. Making it sapient . . . would be bad.
If you didn't read the actual powers, I've only made it immune to three powers: Mind Control (you can't make it do something mentally), Mind Probe (you can't get information from its brain) and Mind Reading (you can't know what its thinking). I didn't make it immune to other mental, or mentally-defined powers. Its Will of 14 simply makes it, potentially, difficult for some Will-based powers to work on it, but it can still be affected. And, as MonkeyFist points out: "Mind Control is one of those powers that, if it works, makes the rest of the party irrelevant. Better to make one character powerless than all but one." Plus, if the Blue Demon could be mind controlled, it would just be a minor nuisance, and not a force of nature. So, psionics with psychic attacks and other abilities, will still be effective against it.
A dedicated mind controller would be in a lot of trouble against the Blue Demon. But, they'd be equally screwed against a robot or a zombie. The more narrow the character's focus, the less effective they will be, over all.
On the other hand, I do like the Detect (Things trying to hurt me, Reflexive). But, I think Dark Vision, or at least some night vision, wouldn't be out of place.
Also, the Blue Demon, while sentient, is far from sapient. GURPS makes the distinction that many people and games don't. You have to have an IQ of 6+ to be sapient (Character, box, pg 23), and the Blue Demon only has an IQ 4. It isn't sapient. Sure, it can feel pain and has emotions (usually in the "RAWR! CRUSH! KILL! DESTROY! TORTURE!" area), but it isn't sapient. Making it sapient . . . would be bad.
If you didn't read the actual powers, I've only made it immune to three powers: Mind Control (you can't make it do something mentally), Mind Probe (you can't get information from its brain) and Mind Reading (you can't know what its thinking). I didn't make it immune to other mental, or mentally-defined powers. Its Will of 14 simply makes it, potentially, difficult for some Will-based powers to work on it, but it can still be affected. And, as MonkeyFist points out: "Mind Control is one of those powers that, if it works, makes the rest of the party irrelevant. Better to make one character powerless than all but one." Plus, if the Blue Demon could be mind controlled, it would just be a minor nuisance, and not a force of nature. So, psionics with psychic attacks and other abilities, will still be effective against it.
A dedicated mind controller would be in a lot of trouble against the Blue Demon. But, they'd be equally screwed against a robot or a zombie. The more narrow the character's focus, the less effective they will be, over all.
On the other hand, I do like the Detect (Things trying to hurt me, Reflexive). But, I think Dark Vision, or at least some night vision, wouldn't be out of place.