Solution to 19D has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Old cake chewed several times in a nursery rhyme! (4-1-6-3) COCK-A-DOODLE-DOO {OLD+CAKE}* [Letter Bank]
Cock a doodle doo!
My dame has lost her shoe,
My master's lost his fiddling stick
And knows not what to do.
My dame has lost her shoe,
My master's lost his fiddling stick
And knows not what to do.
10 Phantom and beloved leader of Freljord cycling (5) UMBRA (-bra)UM(+bra)BRA
11 Warrant for a soldier's slogan? (6,3) BATTLE CRY [CD]
12 It's absurd, cheat is stealing Knight's tape (5-2) STICK ON {ITS*}{C{K}ON}
13 Oafs fly? Suspect dismissals (7) LAYOFFS*
14 An adult insect's study of mind (5) IMAGO [DD]
16 Poor wife is hot and sickly (9) UNHEALTHY UN(-w+h)HEALTHY
19 Cryptically could I set something most murky? (9) CLOUDIEST*
20 Brand mounted without hype in the end (5) SCALD SCALeD
22 Yes! Sen ceased to smuggle substance (7) ESSENCE [T]
25 Love poem with English guide (7) OVERSEE {O}{VERSE}{E}
27 Mariner (colony resident) uncomfortable at first with return of a large spider (9) TARANTULA {TAR}{ANT}{Un...e} and {A}{L}<={
29 Pi loves sex and dangerous stuff? (4,10) HIGH EXPLOSIVES {PI+LOVES+SEX}* [RA]
DOWN
3 From the beginning King never appreciated Chief Kattappa's talent (5) KNACK Acrostic
4 Bond's drone we hear is in the grips of an implant (9) DEBENTURE {DE{(~bee)BE}NTURE}
5 Outcast weasel regularly ignored characters in a number system (5) OCTAL {OutCasT+weAseL}
6 Spooner expresses surprise and lingers in lounges! (9) LOLLYGAGS (golly lags to lollygags)
7 In recess resisted beverage (5) DECAF<=
8 Heard about Indian Classical Dance's epic journey (7) ODYSSEY (~odissi)
9 Naughty smile describing basically unpalatable food (6) MUESLI {M{Un...e}SLI*}
15 Fiat, Quebec Nani drove essentially in reverse (9) ORDINANCE [T<=]
17 Controversial party game? (3,6) HOT POTATO [DD]
18 Camouflaged terrapins come to light (9) TRANSPIRE*
19 Caught a shark, a zooming beast (7) C?E?T?H ()
21 Discover medical practitioner on line (6) DREDGE {DR}{EDGE}
23 Superb! Iago appearing in every other shoot (5) SPRIG {SuPeRb+IaGo}
24 Prepare one-liner supporting establishment at first (5) EQUIP {QUIP}<=>{Es...t}
26 To some extent clergymen voice author's concluding words (5) ENVOI [T]
Reference List
Knight = K, Wife = W, Hot = H, English = E, Large = L, Old = O, Boy = B