It's lucky mother's gone to bed (6)
I believe the answer is:
mascot
'it's lucky' is the definition.
I know that 'lucky' relates to this answer.
'mother's gone to bed' is the wordplay.
I cannot really see how this works, but
'mother's' could be 'mas' (ma can mean mother) and 'mas' is present in the answer.
'bed' could be 'cot' (cot is a type of bed) and 'cot' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mascot that I've seen before include "Thing considered to bring good luck" , "Good luck token" , "Something considered to bring good luck" , "Does it get you first place" , "Character or object used to bring good luck, or represent an organisation" .)