Weird Y (8)
ATYPICAL = Definition is "Weird", Wordplay is an anagram (weird) for "CAPITAL Y".
Strange non-uncle, perhaps? (4)
CLUEMy original guess was RARE, which seems to be the correct answer, but MOehm gets credit for the better explanation.
Combining everyone's answers, and applying MOehm's theory, this is the meta puzzle:
Strange non-uncle, perhaps? (4) = RAR{E} (credit: MOehmcredit: MOehm)
One ton one under sun begun, perhaps (10) = MONOTO{N}OUS (credit: Neil Wcredit: Neil W)
Weird Y (8) = A{T}YPICAL
Mixing endless accessories (5) = BL{I}NG (credit: Neil Wcredit: Neil W)
Disconcerting major exit! (6) = ES{C}APE (credit: F1Krazycredit: F1Krazy)
Perhaps, a resting spot with an eccentric, eccentric start (9) = PERCHANC{E} (credit: MOehmcredit: MOehm)
Direct, and headless (7) = CO{M}MAND (credit: Techidiotcredit: Techidiot)
Perhaps, every permuted tie and portion (12) = ALLIT{E}RATION (credit: MOehmcredit: MOehm)
Under-emphasise (9) = U{N}DERLINE (credit: MOehmcredit: MOehm)
Gained for the first mixture with. (8) = PROFI{T}ED (credit: MOehmcredit: MOehm)
Meta puzzle: When you put together the selected letters (at the letter position equal to the number of words in the clue), you get ENTICEMENT!