The kind of party Reg gets up will simply amaze! (7)
I believe the answer is:
stagger
'amaze' is the definition.
(staggering is a kind of amazing)
'the kind of party reg gets up' is the wordplay.
'the kind of party' becomes 'stag' (I've seen this in another clue).
'gets up' says the letters should be written backwards.
'reg' written backwards gives 'ger'.
'stag'+'ger'='STAGGER'
'will simply' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stagger that I've seen before include "Walk unsteadily, from weakness or drink" , "Totter" , "Reel - astound" , "Pitch" , "Walk as if drunk" .)