Vine ogres rock
Lvl 3 conjuration(vine ogres) and lvl 2 construction(vine crown) is all you need.
And a nature friendly nation like pangaea and you can start pumping out 5(resources gotten per turn from basic pangaea) 10 of em per turn with 5 pans/pando's with vine crowns.
When your territory expands and you find more nature gem resources you might wanna make treelord staves and put more pans/pando's on summoning you can outsummon Ermor even with units that cannot be banished
