Fill in the whole grid with letters, the black lines mean letters are not connected.
I've double checked it and think it's OK.
Across
1 & 4 Copper saves Mim
7 Writer initially sounds like a wigwam - half
11 Oxtail for the king
12 Drug found in drugs laboratory
13 Ogre be changed into an animal changer
15 Jackrum when he was a boy
17 90 degrees missing makes only half a wizard
18 Russian "ov" in Dwarfish
19 The fruit bat is 100.
20 Susan's chum sounds like a fast German
21 Initially a backward football team two times for a dancer
Down
1 Bunches of holly contain drink for the butler
2 Question small hesitation in created book
3 I lost the city
5 "Wherefore art thou Romeo?" asked Gretelina.
6 It's Nobbs - strange wizard
8 Not fussy who he steals from
9 Angua's baby
10 Teacher who betrayed her school
12 Cockney takes a look at footwear
14 Sounds like swamp dragon with note for troll's wife
16 Half a baker round bread missing
Thanx Poohbcarrot , a bit of quiz therapy is just what the doctor ordered. 
