With access to blue, this lets you keep up the threat of counterspells, removal, or something nasty with Flash, and if you dont end up needing to use any of that, you get to play this at the end of an opponents turn and untap further ahead in cards and/or mana
Tymna the Weaver isnt only easier to play, but can also give a significant amount of card draw
And of course, it ties well to specific set mechanics, like delirium or eerie
In addition to being the new lord of the undead, the Dimir god could also prove worthwhile as a mill commander
Repeatable damage is pretty slick
She has been run in Modern for her ability to find Colossus Hammer in Hammer Time, and shes been run in Legacy to find and cheat out any number of Equipment with powerful ETBs with no timing restrictions in Death and Taxes (sure, I GUESS in addition to other Stoneblade decks)