For me, one aspect of a good clue is when I struggle to solve it and then wonder why afterwards because it seems so obvious and there was no shortage of such occurrences in this puzzle which took me slightly longer than usual for a Beelzebub.
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Across
4 Advance with net, grabbing end of unprotected area on underside of tail (9)
SUBCAUDAL – SUB (advance) CAUL (net) around (grabbing) [unprotecte]D (end of unprotected) A (area)
10 Governor’s country house vacated by duke after pressure (5)
PACHA – P (pressure) [d]ACHA (country house vacated by duke)
11 Suckers returning and letting copper in (6)
OSCULA – ALSO (and) reversed (returning) around (letting … in) CU (copper)
12 Note missing European in international assembly, wrongly (9)
IMMORALLY – M[e]MO (note missing European) in I (international) RALLY (assembly)
14 Observe, full of eccentricity, wizard initially very angry in Oz (5)
SPEWY – SPY (observe) around (full of) E (eccentricity) W[izard] (wizard initially)
15 Act evasively, ignoring king in gathering (4)
SHIR – SHIR[k] (act evasively, ignoring king)
16 Man’s turn playing Hamlet? Out of this world (12)
TRANSMUNDANE – an anagram (playing) of MAN’S TURN plus DANE (Hamlet?)
17 System controlling heat in gun going round and round (6)
REGULO – LUGER (gun) reversed (going round) O (round)
22 Bob up and down and spar, boxing very quietly (6)
POPPLE – POLE (spar) around (boxing) PP (very quietly)
23 Dutiful, carrying sceptre, one rejected nonsense seen as disloyal (12)
PRODITORIOUS – PIOUS (dutiful) around (carrying) ROD (sceptre) I (one) ROT (nonsense) reversed (rejected)
25 Cupbearer? Take place next to ambassador (4)
HEBE – HE (ambassador) BE (take place)
26 Collection of tips from Conservative backing marketplace (5)
TRONC – TRON (marketplace) C (Conservative)
28 Publication by fool, unskilled, not right size (9)
MAGNITUDE – MAG (publication) NIT (fool) [r]UDE (unskilled, not right)
29 Skirt worn by Maoris more and more (6)
PIUPIU – PIU (more) PIU (more)
30 Look back and study past (5)
OLDEN – LO (look) reversed (back) DEN (study)
31 Dread previously disastrous stage rounding headland (9)
GASTNESSE – an anagram (disastrous) of STAGE around (rounding) NESS (headland)
Down
1 Refrain from false hope, supporting turbulent priest (10)
EPISTROPHE – an anagram (false) of HOPE under (supporting) an anagram (turbulent) of PRIEST
2 Beat victim, primitive vertebrate (7)
LAMPREY – LAM (beat) PREY (victim)
3 Top mark? Great to receive that (4)
ACME – ACE (great) around (to receive) M (mark)
4 Quibbles raised about method being exposed (5,2)
SHOWN UP – PUNS (quibbles) reversed (raised) around (about) HOW (method)
5 Filler in broadcast about men, fit (12)
BEAUMONTAGUE – an anagram (broadcast) of ABOUT MEN plus AGUE (fit)
6 Cats in company scowl and spit on ground (12)
COLOURPOINTS – CO (company) LOUR (scowl) plus an anagram (ground) of SPIT ON
7 Fictional lion beginning to talk obliquely (6)
ASLANT – ASLAN (fictional lion) T[alk] (beginning to talk)
8 Artist in hovel consuming tea (7)
DUCHAMP – DUMP (hovel) around (consuming) CHA (tea)
9 Comprehensive upset in election I’ll analyse (3-2)
ALL-IN – hidden reversal (upset in) ‘electioN I’LL Analyse’
13 Muttering, not bound to cover miles on trail (10)
FREMESCENT – FREE (not bound) around (to cover) M (miles) plus SCENT (trail)
18 Bog soul scrambled round (7)
GLOBOUS – an anagram (scrambled) of BOG SOUL
19 Stirrer in Scotland being furious lets rip (7)
SPIRTLE – an anagram (being furious) of LETS RIP
20 Place short of American household goods (7)
PLUNDER – PL (place) UNDER (short of)
21 Poem’s gods zero in, protecting leader of Argonauts (6)
DIZAIN – DI (gods) Z (zero) IN around (protecting) A[rgonauts) (leader of Argonauts)
24 Sorcerer’s last assistant turning up in form of worm (5)
REDIA – [sorcere]R (sorcerer’s last) AIDE (assistant) reversed (turning up)
27 Instruments supplied by society for student productions (4)
OUDS – double def.
I started this on a train on the post-Christmas journey home and was pleased to get about half of it done without any aids. Completed it fairly quickly when I got home.
Except. 21dn I knew the word SIXAIN and assumed it must be that, even though I couldn’t parse it. Never heard of DIZAIN, so thanks for the explanation.