We don't see NS often, but this one felt similar to the last one. Dubious anagram indicators, repeated mechanisms ("seaman", "almost all"). At the same time, maybe that's just their thing. 9A had the double wordplay going on and 8A had the semi-&lit. BIBELOTS and AGOUTI were nicely clued for completely unfamiliar words! 25A has an incorrect enumeration, so maybe the editor just sailed it through.

Across

8

Haply ring flange in an Australian tree-dwelling marsupial (6,9)
FLYING PHALANGER — anagram (haply?) of HAPLY RING FLANGE

9

Opening tool with gold and first go at water in cake with cream (6)
GATEAU — GATE (opening tool) AU (gold); G (first letter of gold) AT EAU (water)

10

Seasoning or, for example, an initially optional spices (8)
OREGANOS — OR EG (for example) AN OS (first letters of optional spices)

11

OK in narrow fastening cord passing the hand lightly over the surface (8)
STROKING — STRING (narrow fastening cord) containing OK

12

Confused with a doctor, went to the front (6)
ADDLED — A DD (doctor) LED (went to the front)

13

Seaman employing but doing a lot of harm to (7)
ABUSING — AB (seaman) USING (employing)

16

Leaves behind the barren, dry areas (7)
DESERTS — double def.

19

Seaman has a setback but it grows less (6)
ABATES — AB (seaman) A reversal (back) of SET

21

Harshness from cray bite (8)
ACERBITY — anagram (from?) of CRAY BITE

24

Shocking almost all take up weapons in first group (8)
ALARMING — AL (all without last letter) ARM (take up weapons) IN G (first letter of group)

25

Make a quick reply in the liquid-distilling vessel (6)
RETORT — double def.

26

Entreat year-long busy chief law minister (8,7)
ATTORNEY GENERAL — anagram (busy) of ENTREAT YEAR LONG

Down

1

Plan it! Can be easily directed (6)
PLIANT — anagram (can be) of PLAN IT

2

Previous change could turn poisonous snake-like (8)
VIPEROUS — anagram (change) of PREVIOUS

3

A type of rodent with a joint inflammation, one (6)
AGOUTI — A GOUT (joint inflammation) I (one)

4

The endless and rough from side to side (7)
THROUGH — TH (the without last letter) ROUGH

5

Make unfriendly almost all that is roughly neat (8)
ALIENATE — AL (all without last letter) IE (that is) anagram (roughly) of NEAT

6

In the left and a long distance from the ocean (6)
INLAND — IN L (left) AND

7

The furthest away are oddly mere tots! (8)
REMOTEST — anagram (oddly) of MERE TOTS

14

Stole baby’s meal requirement, returned with household ornaments (8)
BIBELOTS — reversal (returned) of STOLE BIB (baby's meal requirement)

15

Without knowing, changed since ten (8)
NESCIENT — anagram (changed) of SINCE TEN

17

I’m better but still make a sharp taste (8)
EMBITTER — anagram (but still?) of IM BETTER

18

Army gas made from South American striped feline mammals (7)
MARGAYS — anagram (made) of ARMY GAS

20

Start operating or put the top large tea and coffee maker in operation (4,2)
TURN ON — T (first letter of top) URN (large tea and coffee maker) ON (in operation)

22

Listener on the North East right is making money (6)
EARNER — EAR (listener) NE (north east) R (right)

23

Road surface binding material for a car-mat (6)
TARMAC — anagram (material for?) CAR MAT