in other cases, when a creature is put onto the battlefield attacking, that creature's controller chooses which player, planeswalker, or battle it's attacking
I imagine the best way to use this is to identify someone else at the table who would really want a new hand, see how much mana they can assist you with, and then leave only enough mana to cast Game Plan with assistance
Five mana is expensive enough that you probably wont be able to afford any follow-up creatures, but this is still something you can play into if you dont commit too many of your own creatures to the board before you cast it
In fact, most the good decks were creature typal except for Alexander Haynes out of the blue(white) miracles deck which won Pro Tour Barcelona in 2012
Meloetta ex Special Illustration Rare (Black Bolt) Meleoetta ex is the first SIR card revealed in English from Black Bolt and White Flare
The Artifact Creature limitation also means plenty of green Creatures that normally can make use of +1/+1 counters (Pelt Collector, Kalonian Kydra etc.) will just be less useful