His True Magical form doesn't really have any new abilities. His magical power is basically just pure destructive capabilities. As for existence erasure he doesn't have that. At the most he can completely destroy one's body but that's it.
The Supreme Deity cursed Meliodas with Immortality as his punishment, reviving him every time he died in exchange for his emotions being consumed more and more until return to be the bloodthirsty demon he once was.
Possible false alarm causes Fossil fuel-burning appliances may not be burning fuel completely. Check pilot lights/flames for blue color. Appearance of yellow or orange flames indicates incomplete combustion—a source of carbon monoxide.
A CO alarm that beeps continuously without stopping could indicate that carbon monoxide is present. If you your CO alarm is sounding continuously and you have signs of CO poisoning such as dizziness, headache, vomiting or flu like symptoms, find fresh air and call 9-1-1 immediately.
4 Beeps and a Pause: EMERGENCY. This means that carbon monoxide has been detected in the area, you should move to fresh air and call 9-1-1. 1 Beep Every Minute: Low Battery. It is time to replace the batteries in your carbon monoxide detector.