Comet Stellar Puppet is not a Magic the Gathering card, not doing what Magic cards are supposed to do.
Therefore, it shouldn't be included in the peak Mtg experience that is Vintage or Powered Cube.
Let me explain.
Magic cards do the actual thing that's written in the card, are predictable, synergize with other cards, are capable of creating an eviroinment where the more you think, the better are your results. This is still true for the most broken cards.
Dying to a turn 1 channel ulamog lightning greaves is ok. This is what you can predetermine by reading the cards. Mox land channel ulamog greaves is a t1 win, except for opponent's free interaction, or solid t1 interaction.
Comet Stellar Puppet: When it comes in to play you may either make two 1/1 haste creatures, or deal infinite damage, or create infinite 1/1 haste creatures, or whatever.
It just depends by a dice rolled by a computer (not to mention that computers can't produce real randomness, but this is another topic).
This ruins the Powered Cube experience, at least for me.

Ps:
Yes, I did die to a t2 channel eldrazi stuff and to a t4 puppet that killed me out of nowhere. The fact is that t2 channel eldrazi is alwayw going to kill me the same way, while that t3 dog could have just done nothing. This is unacceptable