Each clue is a "sequel" to or "little extra bit" from a previous Ryan's #EnigMarch 2024 puzzle's format, and must be interpreted according to the same rules as that previous puzzle in order to extract the correct letter. Enable Puzzled Pint Mode to see the day numbers and follow along.
Oh by the way this is spoilers for a bunch of the previous puzzles.
Day 6 (ROUND): "Sir Ennedy" sounds like "serenity," and the name tag indicates we should pull out the letter T.
Day 11 (BRIDGE): In the card code from that puzzle, the five of spades stands for the letter E.
Day 1 (DOOR): Bart and Lisa Simpson's principal is SKINNER, and the doubled letter is N.
Day 3 (MUSICAL): The instrument being played is a piano, and the first letter is P.
Day 23 (NEITHER): Lydia doesn't like anything Beetlejuice offers, and his options use every letter except M.
Day 5 (SIGN): The dream described is from the movie Inception, which matches with BUCHAREST at the letter C.
Day 24 (POWER): 169 is THIRTEEN raised to the second power, so we get the letter H.
Day 21 (MIX): If you give Zess T. a Keel Mango and a Peachy Peach, she'll whip up a FRUIT PARFAIT, and the letter to extract is A.
Day 17 (ANCIENT): Use this treasure map the same way you used the Day 17 treasure map, as an overlay onto my puzzle from #EnigMarch 2022 Day 6 (ISLAND). The spot X marks is the letter N.
Day 2 (FALSE): The crossword clues must be taken as false. Northeast, southeast, etc. are not CARDINAL directions; lawful, chaotic, etc. are not NEUTRAL alignments. If you put these in the Day 2 puzzle's grid, they intersect at the letter N.
Day 10 (ZERO): Dark Samus's up smash attack is described. The up smash attributed to Samus belongs to ZELDA, and the up smash attributed to Zero Suit Samus belongs to PEACH. They match at the letter E.
Day 4 (SHIFT): "NOW I AM THE RULER!" is an ability on the Lorcana card "Ursula - Sea Witch Queen" (which had not been revealed at the beginning of #EnigMarch 2024!). Ursula's Shift cost is 5, so take the letter L.
Day 16 (HAND): Take the odd-numbered or "left" letters of "RU EI VY OR LO VE EA RL OR CR EO LE OA TH" to get REVOLVER OCELOT. Who cut off Revolver Ocelot's right hand? The CYBORG NINJA. The letter to take is J.
Day 28 (COIN): The bull and the lady appear on the two-euro coin of Greece. The second letter of GREECE is R.
Day 15 (3D): The words clued are ENCYCLOPEDIA and RHODODENDRON. The letter of ENCYCLOPEDIA that lines up with the third D of RHODODENDRON is E.
Thus we get the phrase TEN PM CHANNEL JRE. This points us to Day 7 (WATCH), the puzzle that was a TV Guide page. Airing at 10:00 PM on JRE is a program entitled "Overspill," so the answer is OVERSPILL.
(no it was not there all along)