Notion Thief steals much more than the thought of a good meal in Commander, where it regularly pinches peoples card draw, and sometimes combos with wheel effects to make everyone really, really hate you
You can, and probably will run your mundane mana rocks, but artifact decks have access to a host of powerful cost reducers that work exceptionally well with broken combo strategies
Ursulas Lair has been seen before, far in the background of the art for Jolly Roger Hooks Ship
As part of the games streamlining of set legalities, products are being split between eternal-legal, or legal in all formats, with Universes Beyond being legal in all formats
It's just that Jeskai Ascendancy and Invasion of Segovia are too good to not build around -- in the end I even added a tutor for them, Drift of Phantasms which can transmute to find either of them, and Moon-Blessed Cleric specifically to find Ascendancy
While it has fallen from grace quite a bit in recent years, being able to search for any land every turn cycle is both incredibly powerful and easy if you arent the player who went first in your pod of players, as youll, in theory, always be behind in land if the first player never misses a land drop