A definite duo from the outset, the winners of Supreme Genesis 1 were always intended to be at their best when used together.
As suggested by their creator: "Use Green Curtain to lock down enemies so Acorn can use her Hurray for the Trees power. This gives Father Oak even more damage potential when he charges in."
Following the Errata in the Guide that made Father Oak Immune/Hurray for the Trees, then it becomes even more of a destructive tactic.
Don't forget also that both are Immune to the restraining effects of Father Oak's Green Curtain Action.
Keep Acorn in Base to Base with dear old dad (a.k.a. Father Oak), and assuming she survuves an attack Father Oak can Strike back out of sequence. Of course this is not limited to Father Oak, but given his protection from Hurray for the Trees, then it is ideal to keep this pair close together.