Answer:
Curtail me thrice I am a youth; behead me once a snake; complete I'm often used in truth when certain steps you'd take.
Everyone asks for me but yet everyone hates to face me. For someone I am agony, for others I am relief! What am I?
I can be short and sometimes hot. When displayed I'm never cold. What am I?
I work when I play and play when I work
In a tunnel of darkness lies a beast of iron. I can only attack when pulled back. What am I?
Give it food and it will live, give it water and it will die.