There is now a way to disable mob spawns:
Download the latest version of the plugin Here and make a new flagset like so:
/foxguard create flagset <flagsetname> passive
If you want to disable hostile mob spawns:
/foxguard modify flagset <flagsetname> set spawnmobhostile false
Likewise for passive mobs:
/foxguard modify flagset <flagsetname> set spawnmobpassive false
Then go ahead and link your spawn region with this new region.
/foxguard link <spawnregionname> <flagsetname>
or if you want to disable it globally:
/foxguard link _global <flagsetname>
Note that these are passive flags, and it won't stop players from using spawn eggs or chicken eggs.
However Simple FlagSets block user caused events instead, and can be used to block spawn eggs.
Use the two together if you want to block both.
EDIT: VERSION 0.9 AND LATER CALL FLAGSETS "HANDLERS" NOW. Anywhere you see
flagset just replace it with
handler and it will work the same as before.
EDIT2: CURRENT VERSIONS OF FOXGUARD ARE COMPLETELY DIFFERENT. NONE OF THESE INSTRUCTIONS WORK ANYMORE.