Laning Phase all active items can be instacast inside of burrow
The Cheese Begins only buy extender + vulnerability if you have the slots in advance, torment pulse is more important
The Powerspike
Build when convenient Use phantom strike while burrowed or to ult
Late Game Options lots of options that fight over active slots so curse and refresher are optional but very good upgrades
Mo & Krill Skills Order

+
+
+
+
1
2
1
5
2
5
1
2
5
1
2
5

+
+
+
+
1
2
1
5
2
5
1
2
5
1
2
5

+
+
+
+
1
2
1
5
2
5
1
2
5
1
2
5

+
+
+
+
1
2
1
5
2
5
1
2
5
1
2
5
Build Description
Active items (including Phantom Strike) can be instantly activated in Mo's Burrow. This build plays heavily around his 2 and ult so that he can absolutely melt enemies.