can i activate enemy controller during my draw phase, steal an opponents monster, sac my treeborn frog, have their monster on my field, and then return treeborn frog to my side of the field during my standby phase.

yes you can as long as you set it last turn because it's a quickplay spell.

You don't need to set it a turn before. During your own turn, quickplays can be played from your hand during any phase.

That is not true. Quick-Play Spells can be activated at any time during your turn, even during the Damage Step if they alter ATK or DEF or specifically allow it.

In this case, even if Enemy Controller was in your hand, you CAN activate it during the Draw or Standby Phases, tribute Treeborn Frog to steal an opponent's monster, and then Special Summon Treeborn Frog again.

That is indeed a legal play since you haven't left your Standby Phase.

He could just play it from his hand, you know.

EDIT: Dang it, too slow.

Not only can you do this, the most memorable defeat I ever suffered was because of a play like this. He opens with a set to each zone. I open with cyber dragon, yaichi and grandmaster. I activate yaichi, and he chains ceasefire. I lose 2000 and procede to hit him for 2100. (his facedown, now faceup was treeborn for the record).

His standby phase. He ponders a while. Brings back treeborn, activates EC to grab grandmaster. brings back treeborn, activates a second EC to grab my cyber dragon. Brings back treeborn in attack and enters his main phase. He plays creature swap, takes my yaichi and gives me the frog. Sacs the yaichi for a cyber dragon ...

ouch
blue that had to suck