Ok here's a little guide on how I play Oak for endgame Godlike.

Items:

Favor : speed +15%.

(In order)

-Monks or Second plate.(depends if I have a support DG with me).

-The 1500g Trinket that gives mana and a chance to proc the 250 arc lightning

-Upgrade to bishops

-The 3300g Gauntlets that gives critics.

-GodPlate or Mage Slayer depending on how well I tank, if they do too much dmg then godplate otherwise Mage Slayer

-Ashkandor(18k)

Anyway it's not a fixed build, if I have mana trouble I'll buy some hats etc.

Skills:

I start with Penitence, then the skill that heals everybody when you last hit. Then I take the Weapon Dmg upgrade, then spirits lvl1, after that I raise penitence and heal to max as well as weapon dmg, and I finish with spirits.

If I die a lot I'll buy berserk or Invuln too, otherwise stats.

Gameplay:

Usually you'll have to endure early game, try to get some kills if you can otherwise just stay with the creeps and lvl up. Once you have the Heal skill lvl2 and the Lightning proc you'll have no trouble killing another DG. Just stay in the middle of the ennemy creeps and hit the hero, sometimes the proc will trigger and kill the creeps healing you for 60-120hp per creep. I usually chase a lot since I can regen when I kill him so if you're certain to be able to kill don't hesitate to chase under towers.

Once you have spirits lvl 2 and more and the crit gauntlets, it gets a lot easier, just stay with the creeps and kill everything on sight.

Don't forget to push N frequently to select all your spirits and order them to attack with you. If you're in difficulty in a fight, try to lure him into his creeps you'll regen while killing him. And if no creeps around, just run under your towers, recast your bishops they'll heal you right away.

Against TB I usually take the Invuln shield lvl 1 around lvl8 and shield myself before i get hit by the bolt it helps a lot.