I posted this to show to different highly playable oak builds. I just thought that we both executed our builds very well.

Some low cost items are very effectiv for their price (I'm thinking: Scaled, Scalemail, Banded). Instead of having 3 or 4 empty slot I suggest filling up all slots, then replacing one item at a time.

The assasin oak has alot of diversity and counter measuring, and buffs against the minions. The problem of full focus minion build is that you won't get any of these for a very long time. I believe it's worth it to sacrifices some damage for more survivability (shield), maybe soulpower I. I'd cut down on Moral/Pestilence to get these. Also I suggest getting the +10 dmg favor item. It's like 2 levels of Moral.

I honestly haven't tried this, but I think a hybrid having more survivability and only minor dps losses on the minions side could work. What you also want to do with a DPS-monster is constantly push buildings, therefore forcing the enemy to come to you, which in return disburdens the other team members.

But if you get maxspirits you should get atleast soul power I

When I play oak, I tend to play max minion. The only flexibility I give up is Shield which I know is a staple for most oak players. Penetence is used to help chase DGs. Having another DG to help box in or slow the opposing DG really helps but is not necessary for minion oak.

Minion Erebus has an easier time than minion Oak for two reasons. Nightcrawlers have more hp and deal more damage than spirits. Nightcrawlers don't require planting flags to summon.

The advantage Spirits have is that they are flying unites and can take a straight line to their designated target. This can make it easier to chase or allow you to take out targets deep in enemy territory. I've won a few fortress games by sending spirits in against enemy fortresses. Yes, nightcrawlers can do this too but not as well since they have to walk there.