Umbris will be bigger each time you cast it, and you easily win via commander damage by making it unblockable, or by using infinite ETB engines to mill opponents out
This three mana 0/3 is your run-of-the-mill toughness commander, making your creatures assign combat damage based on toughness instead of power
Four mana means that you really need this card to do a lot of work in order for it to be worthwhile
Anything you want to accomplish with Rionya can be attempted with Delina, Wild Mage too, but its much harder to pull off, given she makes a tapped and attacking creature, and given that creature will be exiled at the end of combat which will happen as you move to the next combat phase
Tergrid's Lantern in EDH is very powerful if you need a mana sink, and it gets ridiculous with cards like Nykthos, Shrine to Nyx or Cabal Coffers