Thanks to Monk for the challenge.
Great fun! A few new words for me today. We have both Toscanini and Puccini on opposite sides of the grid (they apparently had a tempestuous friendship), but I don’t see more to it. The grid contains a pangram which is always a nice touch. Many thanks to Monk!

E.G.< (maybe, <retiring) + (SAGE (wise guy) on T (tense) + THEMES (subjects))
STEPS ON (moves against)
‘Issue’ meaning child in this context
CONE (solid object) securing SUM (whole)
Double definition
(TOXIN DATA IN)* (*aberrant)
LEAD IN (intro) before (QUOTING* (*rubbish) about E (English) + S (society))
JACK IN (ditch) + THE PULPIT (above which cloth may go)
EVER (at any time) in (A DISNEY)* (*complex)
CO2 (colourless, odourless gas) expanded
LOO (place to go) around (RE (on) + NZ (New Zealand))
A reference to Shakespeare’s Merchant of Venice perhaps?
[sop]ORIFIC E[legy] (section of)
OPPO (cohabitee) + (I INSTRUCT)* (*somehow)
ELECT (choose) + RA (artist)
TOSCA (opera) joining [me]N IN I[olanthe] (quartet of)
[st]ERN (rigorous, putting ST (good man, saint) down)
Max Ernst is a German artist of the Dada and Surrealist movements.
(RULES ONCE)* (*broken)
SIN (function) on AI (e.g. Claude)
Claude is one Artificial Intelligence application
Mount Sinai is biblical – the place where Moses received the ten commandments written on stone tablets
G (good) + AMI (friend, from French) catching OUR (setter’s and solvers’)
ASP (snake) with (LETHAL* (*bent) bites JUNG (psychologist))
Double definition
The second definition is self-explanatory, and the first British slang for male genitalia
STAGE* (*shifted) ahead of BOUT (fight?)
(IS NERVOUS)* (*criminal)
Australian dialect uses the word ‘souvenir’ as a verb meaning to steal something – usually something small
OVER (several deliveries, cricket) in CUP (container)
(IN + I (international) + C (clubs) + CUP (trophy))< (<being lifted)
RO[b] (nick, almost) keeps ONE (individual)
R (Republican) wearing DOWN (blue)
[16d … like the Lufthansa ashtray we have that somebody once souvenired from an airport lounge]
[Hmm, or the Finnair pillowcases by Marimekko]
24 That Lorenzo, certainly, or perhaps de Medici.
Liked JACK-IN-A-PULPIT, GET THE MESSAGE, ENCLOSURE and NEVER SAY DIE.
Undone by GOURAMI and RONEO, not having heard of either.
Thanks to Monk for the workout and Oriel for dishing up the necessary.
Thanks for the blog , very good set of clues with clever wordplay , JACK-IN-THE-PULPIT is very neat , it is also a type of vase that looks like the plant .
Not heard of Claude but the definition and grid helped , this meaning of SOUVENIRS is new to me but the wordplay and grid helped .
Mr Jock , TV quiz Phd , bags few lynx .
Thanks Monk and Oriel
16dn: I was slightly surprised to see the “down under” marking for the meaning of souvenir, with which I was completely familiar. However, Collins 2023 p 1899 marks the meaning “Austral and NZ euphemistic, slang“, and Chambers 2016 p 1490 has it as “orig Aust and NZ; inf“. Of course, Monk has access to the printed dictionaries, not to my personal vocabulary.
A nice gentle puzzle, but I was surprised to see Jack-in-the Pulpit described as “American”. In the UK, it’s a very common plant in woods and hedgerows, being one of the names for Lords-and-Ladies (Arum maculatum) – also known as Cuckoo Pint and Willy Lily amongst others. There’s even a carving of it in Westminster Abbey which predates the USA by a couple of centuries.
Wasn’t familiar with the meaning of Souvenir but the anagram was easy enough. And similarly, NHO Gourami but it was a solid clue which allowed it to be solved. Not sure why OPPO (opposite number) means Cohabitee….
But thanks to Monk nonetheless.
26ac: Chambers 2016 p 1080 says that oppo is a short form of opposite number, which in turn has a range of meanings including “a person who is allotted to one as partner, opponent, etc; one’s cohabiting or marriage partner; one’s mate”.
Thanks Monk for an excellent crossword. I had to reveal MEAT AND TWO VEG (unfamiliar with ‘tackle’) and couldn’t parse JACK IN THE PULPIT and COO. All else slipped into place without angst with my favourites being LEADING QUESTION, LORENZO, ORIFICE, OPPORTUNISTIC, ELECTRA, and ENCLOSURE. When I saw GET THE MESSAGE I searched in vain for a Nina but settled for a pangram as the ‘extra’ in the puzzle. Thanks Oriel for the blog.
Grazer@6 apparently OPPO is used for cell-mate in prison slang , Fletcher certainly used it in Porridge .
Another fish, another plant, more prison jargon and more UK slang with which I am not familiar.
I was tired and in a hurry, and felt I struggled, although it went in quickly enough. If only I had been able to get the long perimeter clues earlier.
Thanks Monk and Oriel
I was another who hadn’t heard of OPPO as a cohabitee. OPPO is most common over here as political slang for “opposition research,” i.e., dirt one digs up on one’s electoral opponent. I have heard it as “opposite number” too, but in more obvious contexts for that phrase than presented here.
While the J and the enumeration was enough to get JACK-IN-THE-PULPIT, I didn’t understand the parsing at all. Of course it turned out to be much simpler than I was thinking it must be!
I found this difficult but eventually got there, other than for Gourami. This beat me, despite being a keen angler.
I found this challenging. But had an aquarium once when i was little with gourami in it thank goodness. Thank you all
I found this one tough but fair, and a lot of fun.
I had to Google GOURAMI because I wasn’t sure why a French word for friend would be used. I don’t see any indication within the clue, such as “European friend.” Has ami crossed over to English?
A year ago, I was delighted to get a handful of answers in a Monk puzzle, so I’m delighted to finish this one.