ACROSS
 1. <zero> GOOSE EGG = GOO + SEE G_G
 6. <powerful> PUNCHY = PUNCH + _Y
 9. <deputy> SECOND-IN-COMMAND = SECONDING[-g] COMMA {,} (_N + _D)
10. LAD ←RED← = LADDER <fraying fabric>
11. (CONS LOSE)* = COOLNESS <composure>
12. <raise> GROW = G ROW
14. <include unnecessary features in> OVERDESIGN = (.b)O VERDE SIGN(a.)
16. <poem> VILLANELLE = VI LL + AN + ELLE
18. ISN'T* = NITS <eggs>
19. <change organisation of> REFORMAT = REFORM A_T
21. <perversion> MISUSE = IS inside MUSE
23. PARENT HE[-c]TIC ALLY = PARENTHETICALLY <by the way>
24. <reporter> NEWSIE = IE after N_E + W_S
25. <racing track> SPEEDWAY = PEED inside SWAY

DOWN
 2. OP + ←ARE← = OPERA <theatre>
 3. S_ WORDS W ALLOWERS = SWORD-SWALLOWERS <circus performers>
 4. <quilt> EIDERDOWN = (WE'D IRONED)*
 5. <dessert filling> GANACHE = PANACHE, P→_G
 6. <advertisement> PROMO = PRO MO
 7. <saw> NO MAN IS AN ISLAND = (NO, MAN IS AN ISLAND)
 8. HINDS RIGHT - R = HINDSIGHT <retrospect>
13. <recap> REITERATE = REITER AT _E
15. <surreal> DREAMLIKE = (DALI REMAKE - A)*
17. <sails> LATEENS = LA + TEENS
20. <headdress> MITRE = MIT RE
22. ←LAS← SA = SALSA <dance>