In order to be invulnerable from other mind control or hypno attacks, Yasker will have to go as far as mind control himself.

This cause his conciousness and his body to split apart while still maintaining his personality, memories, power and controls. Because it is confusing who is in control right now, this deny all kind of mind controls or hypnotizing from others if they try doing it to Yasker.

And the reason why it called "Sad Form", in this form, he talk a lot about sad things happily.