Functionally, Yuna's Whistle is a pseudo-cantrip that always replaces itself with a creature, and finding the creature gives you some +1/+1 counters too, so there's combat trick potential as well
If you can somehow hit all three opponents or you have double strike then you can generate up to six extra combats that turn
That's not much of a bonus unless your whole deck profits from destroying your own creatures
Simoon is perfect for dealing with creatures like Delver of Secrets, or Thalia, that tip the scales of victory in favor of the opponent
I think until Cutter loses its grip on the format (which might not be for a long time) you can relegate this one to your trade binder, but I might keep it around just in case
Yes, were still waiting for that animated series announced four years ago, but as they say: always leave them wanting more.