Update 1.10.6.4: Beholder The Beholder!

Overhaul: The Shadow Spawn Type (which causes Grues to spawn sometimes
should the light suddenly drop) has been removed, I was never 100%
satisfied with it and a lot of people didn't get it either. In its place
I have added the Darkness Spawn Type where staying in the dark for too
long will eventually spawn Grues, players will be warned as they come
closer to spawning one. This works from light level 4 (night time above
ground) but is fairly rare, at levels 1 and 0 it becomes significantly
more common so stay out of the pitch black! Because of this change, the
configs will need to be reset, you can manually update your config and
then delete the shadowmobs-spawning.cfg if you want to keep things
though.

Improvement: Summoned Spriggans will now cause all nearby crops and
various plants to grow at a very fast rate around them! This can be
configured in forestmobs-general.cfg and can be disabled if desired too.

Improvement: Various events such as Boulder Dash or Root Riot will now
increase the spawn chances of their respective mobs! For example: mining
is even more deadly during Boulder Dash!

Improvement: Increased the speeds of the Summoning Staves.

Improvement: The Stable Summoning Staff now summons a minion for 3
minutes increased from 2 minutes.