Creating never-ending puzzles is positive (7)
I believe the answer is:
certain
'positive' is the definition.
(similar in meaning)
'creating never-ending puzzles' is the wordplay.
'never ending' means to remove the last letter.
'puzzles' is an anagram indicator.
'creating' with its final letter taken away is 'creatin'.
'creatin' with letters rearranged gives 'CERTAIN'.
'is' is the link.
(Other definitions for certain that I've seen before include "Assured" , "bound" , "Sure, definite" , "Particular" , "Known beyond doubt" .)