Solution - Not Quite A Polka

By Charles Steinhardt
Cryptic clues edited by several testsolvers, including: Eggy, Alex Irpan, Nishant Pappireddi, Alex Pei, Diyang Tang, Anderson Wang, and Patrick Xia

In this puzzle, there are two groups of cryptics. The first group has longer words, and is in alphabetical order. The second group is not in alphabetical order, and is much shorter.

Solving enough cryptics from the top and bottom group should reveal why Pinkie Pie is a one-pony band: every cryptic in the first group has an instrument inside it, which can be replaced with a single letter to get a cryptic in the second group.

With decent start, old spirits produced stagnation (8) DOLDRUMS D (decent start) + OLD + RUMS (spirits)
At first, Bond and me returned as spy ring for a foreign mission (7) EMBASSY reverse(B + ME) (first of Bond + ME, returned) + AS + SY (outer letters of SPY), where foreign mission means a building, not a task.
Homeless vagrants who lost head, heartless boxes (6) HOBOES HO (who without head) + BOES (BOXES without X)
Steer far, trim prickly bushes (8) LONGHORN LONG (far) + HORN (THORNS without first and last)
Close to nature or anxiety getting a new good start (7) ORGANIC OR + PANIC (anxiety), start of PANIC changed to G (good)
One who spoils election, mostly external (8) POLLUTER POLL (election) + UTER (most of OUTER)
Like snake, imprisoned purchaser pent in exasperation (10) SERPENTINE Hidden word (imprisoned), puchaSER PENT IN Exasperation
A subtle mix-up produced Portuguese city (7) SETUBAL anagram(A SUBTLE)
Seized half, left following pointy permanent markers (8) SHARPIES SHARP (pointy) + IES (first half of SEIZED, read towards left, following SHARP)
Spend time doing nothing for relaxed durations (3 6) SIT AROUND anagram(DURATIONS)
Novel audit adjustment is sacrosanct (10) UNVIOLATED anagram(NOVEL AUDIT)
Contaminated villa source relating to chickenpox (11) VARICELLOUS anagram(VILLA SOURCE)
Campaign tour is how a soccer match might end? (7-4) WHISTLE-STOP Double definition (whistle-stop campaign, whistle at end of soccer match)

CrypticSolutionExplanationMatching WordLetter
Sounds like I spelled out an award (4) EMMY ME (I), spelled out EMBASSY M
Extreme Arctic or Antarctic (5) POLAR Double definition (extreme, Arctic or Antarctic) POLLUTER A
This ultimately belongs to that guy (3) HIS end of THIS HOBOES I
Loud noise from eagle's head to eat (4) DINE DIN (loud noise) + E (eagle's head) SERPENTINE D
Diverse diversified saviour (7) VARIOUS anagram(SAVIOUR) VARICELLOUS O
Fast troops, oddly, produced a camera setting (1-4) F-STOP Every other letter of FAST TROOPS WHISTLE-STOP F
Fools speckles around central Ireland (5) DOLTS DOTS (speckles), around L (middle letter of IRELAND) DOLDRUMS T
Yellow Pegasi without flapping wings make frightened movements (5) SHIES FLUTTERSHIES (yellow Pegasi) - FLUTTER (without flapping wings) SHARPIES H
She heals every other Water Pokemon (4) SEEL Every other letter of SHE HEALS. SETUBAL E
Missouri edges away investments from dirt pile (5) MOUND MO (Missouri) + UND (FUNDS, without first or last) SIT AROUND M
Brought together flyers (6) UNITED Double definition (brought together, United the airline) UNVIOLATED I
Yearns for covers of love songs (5) LONGS Outer letters of LOve soNGS LONGHORN S
I hear a clock sound like an unconscious quirk (3) TIC TIC is a sound a clock could make (tick-tock) ORGANIC T

Taking the single letters in order of the second group gives the answer MAID OF THE MIST.

Authors Notes

Alex: Charles constructed the first draft of this puzzle, and the core mechanics went through testsolving unchanged. The only changes made were giving answer lengths to ease the difficulty, and tweaking cryptic clues based on testsolver feedback.

For a long time, the SEEL clue's definition half was "prevent from seeing". I liked this, because it taught me SEEL was an archaic word, and not just the name of a Pokemon. Literally every other testsolver did not like this. I defended it for a while, but eventually caved in, since the clue only worked if you decided to check if SEEL could mean anything besides a Pokemon.

Theme-wise, instruments are more of an Octavia thing than a Pinkie Pie thing, but I knew there was going to be a Vinyl Scratch puzzle in Round 2, and it felt better to spread out the music-themed puzzles.