The one cost instant will give River Song a +1/+1 to grow permanently and then phase out for a turn as response to removal targeted like Swords to Plowshares, mass like Blasphemous Act, or combat damage
If you land on tails, however, then all of your Benched Pokmon take 20 damage instead
All he asks in return is food, pets, and a place to play with his favorite teddy bear
Mustering two 2/2 Knight tokens over its first two steps, the saga then provides an Overrun-esque stat buff for all your Knights, which can swiftly end the game with the right setup
Add a Thran Dynamo or Mana Vault with your commander out and you get all the mana
You need another way of untapping them, but you have access to all colors, so it wont be hard