The Consequence of Being Mortal by Phi

Phi's latest offering was sheer pleasure, and just the kind of diversion for a Saturday morning after a night before. The theme was hangovers, or more specifically, P.G.Wodehouse's various and colourful euphemisms for them, which were clued without definition. In an unusual and not previously seen method of entry, each non-thematic across answer "hung over" into the next, that is, each answer was shifted over by one cell so that its last letter appeared at the beginning of the next light. The wordplay to each such clue led to the actual entry, causing the solver much initial confusion with clues that didn't quite seem to work. Once the trick was seen, though, rapid progress could be made.

Redundant letters in the wordplay in non-thematic down clues spelled out "Wodehouse: Mating Season" (and not "Matins Sermon" as Gregson for a while guessed, led astray by fond memories of "The Great Sermon Handicap").

Across
1 Most of local mist blocking mountain (common way through range) (13, two words)
BROKEN COMPASS (ROK minus last letter inside BEN + COM(mon) + PASS)
12 Advantage that is reversed after swallowing narcotic (5)
AVAIL / EAVAI (AVA inside I.E. rev.)
13 Chap with fuel round river held back in dispersal warning (7, two words)
RIOT ACT / LRIOTAC (CAT + R(iver) inside OIL, all rev.)
14 Girl almost in fashion in Italian city (6)
VERONA / TVERON (VERA minus last letter inside TON)
16 Ending of prayer involving name in new rite for burial (9)
INTERMENT / AINTERMEN (N(ame) inside jumble RITE inside AMEN)
17 Time to claim no knowledge of French saint (5)
DENYS / TDENY (T(ime) + DENY)
19 Almost succeed in romantic approach, showing heart (4)
CORE / SCOR (SCORE minus last letter)
22 US city -- somewhere new? Not entirely (4)
RENO / EREN (Hidden in somewhERE New)
24 Mineral cave filled with carbon? It's not worth much (7, two words)
RED CENT / OREDCEN (ORE + C(arbon) inside DEN)
26 Squadrons mass, mostly longing to invade city (13, two words)
SEWING MACHINE (WING + M(ass) + ACHIN(g) inside SEE)
28 What's the point about dull theatre performance? (7)
MATINEE / TMATINE (MAT inside TINE)
33 Activity occupying one's time (4)
STIR / ESTI (Hidden in onE'S TIme)
34 Former BBC chief dismissing one without difficulty in the past (4)
ETHE / RETH (REITH minus I)
The reference to Lord Reith seemed obvious to Gregson but some younger and/or overseas solvers may have been scratching their heads.
35 Disconcert each singer? Not soprano (5)
ABASH / EABAS (EA(ch) + BASS minus S(oprano))
37 Holy areas devastated for a period of time (9, two words)
SOLAR YEAR / ESOLARYEA (Anag. HOLY AREAS)
40 Right to support cut body tissue (6)
TENDON / RTENDO (RT (right) + ENDOW minus last letter)
41 Previous outcomes can seal game (7, two words)
CASE LAW / NCASELA (Anag. CAN SEAL)
42 Prostitutes ignoring English stud? (5)
HORSE / WHORS (WHORES minus E)
43 English money (pounds) invested in snare -- favour mostly Scottish offer (13, two words)
GREMLIN BOOGIE (E(nglish) + M(oney) inside GRIN + BOO(n) + GIE (Scottish give))
GRIN for snare was unexpected -- the much more obvious GIN didn't quite work

Down
1 Computer game trials perhaps ineffectual at blocking defeats (9, two words)
B[W]ETA TESTS (WET + AT inside BESTS)
2 Staff accepting greeting uttered wildly (5)
RAVE[O]D (AVE inside ROD)
3 See preamble
OVER
4 Asian people finish interrupting recipe (new) in New Zealand food (7)
KAREN[D]NI (R(ecipe) + END + N(ew) inside KAI)
5 Title encompassing goblin or dwarf state (6)
NANISM[E] (NIS inside NAME)
6 Family links ignoring one? Line to be included (4)
C[H]LAN (L(ine) inside CHAIN minus I)
7 Speaker I remove from choral work (6)
ORATOR[O] (ORATORIO minus I)
8 See 15 down
9 Turned up with our editor and gushed (6)
P[U]OURED (UP rev. + OUR + ED)
The wordplay would work just as well with or without "Turned", but its inclusion improved the surface.
10 Order of sorts apparent in a nervous disorder (6)
ATOMIC (OM inside A + TIC)
11 Scrutinise self-contained solution, in short (4)
SCAN[S] (SC (Self-contained) + ANS(wer))
15,8 Wanton minx met in church starts to enthral rake (11, two words)
CEMENT MIXER (Jumble MINX MET inside CE + first letters of ENTHRAL RAKE)
18 That? That is a Hindu symbol (4)
YONI[E] (YON + I.E.)
20 Philosopher meeting with slight change (5)
COMET (COMTE with last two letters reversed)
21 Seeing moss clumped with coarse grain (9)
GNEISSOSE[M] (Anag. SEEING MOSS)
23 Assembled paper is including section with errors (6)
R[A]EMISS (REAM + IS + S(ection))
25 See private eye attending church (4)
[T]ECCE (TEC + CE)
27 He has a rival: heroine's first love gets the boot (7)
HEAV[I]E-HO (HE + A + VIE + First letter of HEROINE + O)
29 Assemblies in history almost upheld (6)
AGORAE[N] (AGO + NEAR rev.)
30 One dropped from side, covering both parts of tie as mascot? (6)
TELE[G]SM (LEGS inside TEAM minus A)
31 Is film actress picking up this scented oil? (6)
NEROL[S]I (IS + (Sophia) LOREN)
32 Innocent figure, young reporter, seen around this place (6)
CHER[E]UB (HERE inside CUB)
34 Sort of badger set on climbing rising meadow (5)
RAT[A]EL (TAR rev. + LEA rev.)
35 Mediterranean resident runs island as King (5)
[S]ARD-RI (SARD + R(uns) + I(sland)
37 See preamble
HANG
38 The solver's one that may break down in fen (4)
Y[O]UAN (YOU + AN)
Yuan is a unit of currency = 100 Fen.
39 Carol accepting new cuddle (4)
S(N)ONG (N(ew) inside SNOG