1A: (ASCIPHER)* = SERAPHIC9A: Three articles = AN, A, THE + master = MA -> ANATHEMA10A: First letters of clue = GONEAWOL11A: First two letters removed from FIESTAS = ESTAS12A: Little = L + bit of a roof = EAVE -> LEAVE16A: Key = ESC, two rings = OO, empty T[ot]E, rubbish first = R -> ESCOOTER19A: Striking = STUNNING, swapping time = T for hostages first = H -> SHUNNING20A: Three = THREE, bit more = PI, nothing = O -> THREEPIO
Down:
1D: Laughing = GAS, returning = SAG + eastern = E -> SAGE2D: NOSE, slightly out of joint (anagrind) = ENOS3D: Cut one letter off GRANT = RANT4D: A + shade of blue = TEAL + ON + Everest's peak = E -> ATEALONE5D: Receiver = PHONE, taking A + direction = SE -> PH[ASE]ONE6D: Grant = Hugh Grant, Hugh sounds like "HEW"7D: One = I, Stooge = MO -> IMO8D: In[CA L]egend contains CAL13D: Flatbread = PITA, flipped over = ATIP14D: IN + Tesla = EV, reversed = VENI15D: Shrek = OGRE, overturned = ERGO16D: (SET)* = EST (anagr.)17D: In styli[SH H]eels -> SHH18D: aCqUiRe, regular letters ignored = CUR
Very gracious of you to fully check a cryptic, and I liked the fill you chose.
Pros:
I disliked 1D at first until [Laughing, perhaps] finally clicked (as something you might find at an old-school dentist's). Nice!
I got a kick out of the duplicate clue at 3D and 6D, enough so that I didn't mind that you were using [Cut] as a beheadment rather than curtailment.
Very nice &lit at 10A, though I think GONE (past) doesn't quite match [Getting out].
Nits:
7D has a neat concept, but the stooges are Larry, Curly, and Moe. I don't see how you get MO here without indicating a deletion.
14D is, I think, missing some indicators. [Tesla] isn't 1:1 with EV, and [I came] is VENI, but I think some sort of indicator of Latin is needed.
16A is cryptically correct, but the surface seems like gibberish; am I missing a reference?
20A has me torn on the use of [a bit more], as it means that [Three] is essentially being used twice. It's an obvious enough answer, and because it's fully checked I think you have the freedom to push the envelope a bit, but it did stick out to me.
Thanks for the feedback! I've modified 7D/14D to hopefully correct for these.
The surface for 16 is a bit disappointing - the best I could come up with was "bag of mixed garbage being got at by a bird", but you've (rightly) sussed out that this was a bit of fill..