The most common and most likely answer to this crossword clue is the 9 plus 5 letter word TASMANIAN DEVIL
I've seen this crossword clue in The Sunday Telegraph
T
A
S
M
A
N
I
A
N
D
E
V
I
L
Buddy explains!
The straight part
We know that "a kind of marsupial" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a kind of marsupial = tasmanian devil.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.