Solution to 13D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
8 Bored by country song in party? (8) CAROUSAL {CARO{USA}L}
9 Way, reportedly, to get to big house (5) MANOR (~manner)
10 European has half Polish name (4) FINN {FINish}{N}
11 What's seen in hands of orthodontists, etc? (3,2,5) AND SO FORTH [T]
12 Overwhelmed by arthritis sometimes? Yes! (2,2,2) IT IS SO [T]
14 The University dean's building is cool (8) UNHEATED {THE+U+DEAN}*
15 Heartbroken chaps continue to sigh? (7) BREATHE {HEART}* in {BE}
17 Hip and leg operation basically pending (2,5) IN LIMBO {IN}{LIMB}{Op...n}
20 Wretched fellow's killing time inside (8) INFERNAL IN(+f-t)FERNAL
22 Play fine puzzle right away (6) FIDDLE {F}{rIDDLE}
23 Ones you can bank on, to get serious? (2,8) NO NONSENSE {ONES}* [Letter Bank]
24 OK to pester for repayment of a loan, we hear (4) DONE (~dun)
25 One of the best violinists ever from Russia, enthralled millions, for starters (5) EFREM Acrostic Semi&lit
DOWN
1 Support staff for flights? (8) BANISTER [CD]
4 Lids came off easily? (4,3) SLID OUT {LIDS}* [RA]
5 Even in those days, dogs primarily scavenged meals on occasion (8) SMOOTHEN {THEN}<=>{Sc...d}{Me..s}{On}{Oc...n}
6 Ordinary and OK? Fine and fantastic? Or exceptional? (3,2,1,4) ONE OF A KIND {O+AND+OK+FINE}*
7 Jerk starts to expose his tummy in restaurant, when getting a tip (6) WRITHE [Acrostic<=]
13 Spooner's hound got a ride (10) S?A?E?O?R?
18 Cat is able to jump around corner (8) BALINESE {IS+ABLE}* over {NE}
21 What's set up quickly, at the conclusions of some trials? (6) NOOSES {SOON<=}{somE}{t...lS} &lit
22 Strong fellow gets hurt unloading piano (6) FIERCE {F}{pIERCE}
Reference List
Name = N, University = U, Fellow = F, Time = T, Fine = F, Right = R, Ordinary = O, Day = D, Corner = NE, Piano = P