Umori's last ability doesn't change the mana cost or mana value of any spell
If your life total is bigger, the Revenge is just gaudier and more obvious
As long as this creature has three or more +1/+1 counters on it, it has flying and is a Knight in addition to its other types
The last ability is a mana ability
The real fun of this card is if you can duplicate the ability with cards such as Naban, Dean of Iteration, Harmonic Prodigy, or Strionic Resonator (or, if you really want to get crazy, all three)
Much like Possibility Storm, you can build a deck around Unpredictable Cyclone in two ways: you can either play it fairly as Garfield intended, or you can put in some extra work during the deck0building process to play it unfairly