Creature of the night drained white bloom from the bottom up (8)
I believe the answer is:
werewolf
'creature of the night drained' is the definition.
I can't tell whether this defines the answer.
'white bloom from the bottom up' is the wordplay.
'white' becomes 'w'.
'bloom' becomes 'flower' (synonyms).
'from' means one lot of letters go next to another.
'bottom' suggests the final letters.
'up' is a reversal indicator (in down clue: letters go upwards).
The final letter of 'the' is 'e'.
'flower'+'e'='flowere'
'flowere' in reverse letter order is 'erewolf'.
'w'+'erewolf'='WEREWOLF'
Can you help me to learn more?
(Other definitions for werewolf that I've seen before include "one bewitched" , "Lycanthrope, shape changer" , "Full moon shape-changer" , "Human who turns lupine at the full moon" , "one who can become beastly" .)