The most common and most likely answer to this crossword clue is the 5 letter word GLOOP
G
L
O
O
P
Buddy explains!

The straight part
We know that "Mawkish stuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mawkish stuff = gloop.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.
What does GLOOP mean?
GLOOP noun- Any gooey, viscous substance.
- To flow like goo or goop, to move in a slushy way.
- To cover someone in gloop or goo.