This puzzle may not have been written for Hallowe’en, but that definitely seems like a good time to revisit it.

A little heavy on the anagrams, in hindsight. Some fun surfaces and a good gag in here, though.

ACROSS

1 BRAINS Inside: Heads of Cobra institute revealed! (6)

Contained (revealed) in CoBRA INStitute.

4 RESIDENT EVIL Trump, Satan lose their heads over a game (8,4)

pRESIDENT and dEVIL, each without their first letters (losing their heads).

11 SKA Two-tone siren keeps alarming at first (3)

Initials (at first) of Siren Keeps Alarming.

12 WINCHESTER Victory at Welsh border town - now let's get a drink and wait for all this to blow over (10)

WIN (victory) + CHESTER (Welsh border town). The Winchester is the name of the pub in Shaun of the Dead.

13 CORDYCEPS Decoy’s chest compression mix-up leaves a real fun guy in control (9)

Anagram (mix-up) of DECOY + CPR (chest compression). Cordyceps is the fungus which creates ‘zombie ants’.

15 ORALLY "Instead, make friends" spoken aloud (6)

OR (instead) + ALLY (make friends).

17 TOP BANANA Highest fruit is best of the bunch (3,6)

Double definition.

20 BODY Rambo, dying, reveals figure (4)

Contained (reveals) in RamBO DYing.

21 ILL One and two learners doing poorly (3)

I (one) + LL (two learners).

23 TASTED Sampled cooked bread wi' nowt taken out (6)

TOASTED (cooked bread) -O (nowt). A reference to the Allinson advertising slogan.

25 E-FIT Identify regularly-reorganised face (1-3)

Anag (reorganised) of alternate letters (regularly) of IdEnTiFy.

28 HOUSE-TO-HOUSE Laurie's doctor in conversation with himself with full coverage (5-2-5)

Gregory HOUSE (played by Hugh Laurie) talking to himself might be described as a House-to-House.

30 RINGMASTER Puts on a show starring me as never before (10)

Anag (as never before) of STARRING ME.

31 ELECTORATE Citizens locate tree, possibly (10)

Anag (possibly) of LOCATE TREE.

34 SALVADOR DALI Sea levee, adored (a lie) without ecstasy by surrealist (8,4)

Remove all the Es (without ecstasy) from SeA LeVee ADOReD A LIe.

36 DIET What goes in is a rough edit (4)

Anag (rough) of EDIT.

38 TAOIST Philosophical one who scratches, less over-the-top (6)

TATTOOIST (one who scratches), removing OTT (over the top).

39 ODE Old Tokyo returns in verse (3)

EDO (old namke for Tokyo), reversed (returns).

40 ABEL Second son found in seatbelt without tests (4)

Remove TESTS from SEATBELT.

42 LYNCH MOBS Crowds turn violent as man of blue velvet disarms explosives without backup plan (5,4)

David LYNCH (director of Blue Velvet) + anag (disarms) of BOMBS, removing B (backup plan).

46 ESSAYS Zombie's balsa flays backs off students' pieces (6)

Last two letters (backs) of zombiES balSA flaYS.

48 PATROLLER Spooner's rodent survey-taker pounds the streets (9)

Spoonerism of RAT POLLER.

49 CAIPIRINHA Messy hair - I panic, get a Brazilian (10)

The delicious Brazilian cocktail is an anagram (messy) of HAIR I PANIC.

50 N.R.A. Fled in disorder from their cold dead hands (1,1,1)

Anag. (in disorder) of RAN (fled). Allusion to the slogan famously used by Charlton Heston at an NRA convention.

52 SLEEPWALKERS Sisters take on were-elk pal in confusion - they're up at night ... (12)

SS (sisters) around (take on) anag. (in confusion) of WERE-ELK PAL.

53 .NAUSEA .. feeling queasy after seeing nana use aftershave (6)

Contained (seeing) in naNA USE Aftershave.

DOWN

2 APOCALYPSE Primate picks up Caribbean rhythm, leading with feet - it's a disaster! (10)

APE (primate) containing (picks up) CALYPSO (Caribbean rhythm), moving the last letter to the front (leading with feet).

3 SPASM Head massage after health clubs will make you twitch (5)

SPAS (health clubs) + M (head of Massage).

4 ROMERO Will’s lover captures cold heart as directed night and day ... (6)

ROMEO (Will’s lover) containing (captures) R (cold heart - heart without HEAT). George Romero directed Night of the Living Dead and Day of the Dead.

5 SOS ... concluding his folio as a cry for help (3)

Last letters (concluding) of hiS foliO aS.

6 DEACON Religious position in undead pack zone central (6)

Middle letters (central) of unDEas pACk zONe.

7 NEURON Cloaked in numbers, federal currency transmits signals (6)

EURO (federal currency), surrounded (cloaked) by Ns (numbers).

8 VINCIBLE 5/100 skip first chapter of a good book - they can be beaten (8)

Read 5/100 as “5 IN 100” and convert to Roman numerals - VINC + bIBLE (good book, omitting the first letter).

9 LIMPED Untruth told, military police in the centre of it went nowhere fast (6)

LIED (untruth told) arround (in the centre of) MP (military police).

10 DAWN OF THE DEAD Fed two-handed, a messed-up classic (4,2,3,4)

Anag (messed-up) of FED TWO-HANDED A.

14 OBITS Love pieces published after death (5)

O (love) + BITS (pieces).

16 YOUTH HOSTEL Lodgings for teenagers - ooh, they lust madly (5,6)

Anag (madly) of OOH THEY LUST.

18 ANTENATAL Before the big event - volcano climbing - it's natural you are withdrawn (9)

ETNA (volcano), reversed (climbing) + NATurAL with UR (you are) removed (withdrawn).

19 AIDE-MEMOIRE Help to recall a meme or I die crazy (4-7)

Anag (crazy) of A MEME OR I DIE.

22 CHINATOWN Drinking with canon in asian district (9)

Anag (drinking) of WITH CANON.

24 AERIAL Sky-high blood pumping away with 40% of heart removed (6)

ARTERIAL (blood pumping away), without RT (40% of heart removed).

26 FAT Tallow could be in the stern (3)

Anag (could be) of AFT (in the stern).

27 THROWING SHADE He's a downright awful one for public criticism (8,5)

Anag (awful) of HE’S A DOWNRIGHT.

29 UNLESS Excepting one French reduction (6)

UN (one French) + LESS (reduction).

32 EYE Examine alternate re-typed (3)

Alternate letters of rE-tYpEd.

33 ADMISSIONS Commercial title, small charges at points of entry (10)

AD (commercial) + MISS (title) + IONS (small charges).

35 ATOMS Maybe stoma are indivisible (5)

Anag (maybe) of STOMA.

37 TOLERATE Put up with sound of the bigger octet (8)

Homophone (sound of) TALLER EIGHT (bigger octet).

41 BRAINS Eno's new composition is matter of taste here (6)

Anag (new composition) of BRIAN + S (from Brian Eno).

43 YELLOW Coward radios a greeting (6)

Near-homophone (radios) of HELLO.

44 CARNAL Without 4, travelling circus leads to knowledge of 20 (6)

CARNIVAL (travelling circus), removing IV (4).

45 BRAINS Underwear, fashionable, supports primary organs (6)

BRA (underwear) + IN (fashionable) + S (first letter of supports).

47 SPAWN Offspring's weakest pieces moving back-to-front (5)

PAWNS (weakest pieces, in chess), moving last letter to the beginning.

51 AXE Singular former lover ascends to the chopper (3)

A (singular) + EX (former lover), reversed (ascends). The surface describes the conclusion of the excellent Dawn of the Dead.