*blanks in the clues had to be filled with a word (or a two-word phrase) that enabled the clue to be solved (these words being also themselves the solution to a clue)
Across
1 baseless [CITY] BASEL/(c)E(n)S(u)S
5 wasted [SEIZE] W<A(s)S(e)T(s)>E’D
10 animation [ECLIPSES] AN<I(odine)/MAT>ION
11 china [BRANCH] branCH IN Amazon (hidden)
12 city [SCI-FI] C(irca)/(sci-f)/I/(ghos)T/(stor)Y
13 Montenegro [HERB] M(i/O)NT/GREEN(anag)/O
15 almost [MONTENEGRO] A/L(arge)<M(ontenegr)O>ST(reet)
16 drained [DIAMONDS] D(iamonds)/RAINED
19 chaotic [TRENDY] CH<A(merican)/O(old)T(estament)>IC
21 Oscars [SPIN OUT] S(tar)/R(esents)/A(gent)/C(hurning)/S(pin)/O(ut)
23 institutes [THING] IN/S(ociety)/IT(rev)/TUTE(e)S
25 hear [SCINTILLA] H(orseradish)/EAR
27 sci-fi [INSTITUTES] S(cholasti)C/I(nstitute)<F(rance)>I(institute)
28 chameleon [CHAMELEON] ME (ie Chameleon) in CLONE(d) HA (anag)
29 sleigh [ALMOST] S(anta)/L(eaving)/EIGH(t)
30 verbally [LEAP] LAB/REV (rev) + L(eap)/Y(ears)
Down
1 branch [DRAINED] BRA + N(ordi)C/H(-bomb)
2 scintilla [CHAOTIC] ILL in ANTICS (anag)
3 leap [CHINA] PA<E(astern)>L (rev)
4 spin-out [UNITED] U(nited) in POINTS (anag)
6 ascendancy [NERVE CELL] A(ctive/N(erve)/C(ell) in SYNCED (anag)
7 thing [BASELESS] THIN(k)/(do)G(ma)
8 diamonds [ASCENDANCY] MAID(rev)/ON/(b)DS(m)
9 united [VERBALLY] you knighted (hom)
14 containing [WASTED] GIN AN(d) TONIC (anag)
17 nerve cell [CHURCH] C(of)E/LL under NERVE
18 eclipses [ANIMATION] LESS EPIC (anag)
20 church [SLEIGH] CHU(m)/RC/(sleig)H
21 operate [CONTAINING] OP(i)<E(cstasy)/R(ight)>ATE
22 trendy [OSCARS] T(oo) NERDY (anag)
24 seize [HEAR] C(rypti)C (hom)
26 herb [OPERATE] (lit)H(ium)/(conv)E(rter)/(ope)R(ate)/(ur)B(an)