Look! Game includes new monster's lair (4,4)
I believe the answer is:
loch ness
'monster's lair' is the definition.
(supposed home of the Loch Ness Monster)
'look game includes new' is the wordplay.
'look' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'game' becomes 'chess' (chess is a kind of game).
'includes' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'chess' placed around 'n' is 'chness'.
'lo'+'chness'='LOCH NESS'
(Other definitions for loch ness that I've seen before include "Scene of monsters?" , "Legendary Scottish apparition" , "Scots monster's home" , "Scottish monster's home" , "waters" .)