Let’s talk about why playing as Oak in Plants Vs Zombies takes lots of skills. Right now, the new TTK is live from the latest update. And being an Oak takes about 35 damage on critical hits. Here are the reasons why Oak are the best hero but you need skills to play him.
Once you're low health you can eject as Acorn.
I suggest you exit when you’re about half way on your oak health. Before the update, once you exit and be an Acorn, you would have 125 health as Acorn. But now it will stay as your current health.
Sap trap are very important in getting kills. Especially, if you see your enemies’ health about third quarters of the way. OAK has 125 damage from the sap trap. Exit as Acorn to immediately gain 60 damage from Acorn small sap trap.