The refrain cards both look pretty interesting — not sure if I'd be interested in them for cube, but I was always fond of Arc Blade et al.
Surge to Victory is literally designed for one of my pet decks. Too bad that I decided to make it Modern legal, otherwise people would get
drowned under copies of Magma Opus.
This is an interesting card for a spell-slinger archetype. Note that you get to keep any instant or sorcery cards that you hit other than the one you cast.
And finally, we have this cycle. Sure, it relies on multiplayer politics to work, but Demonstrate is a pretty interesting mechanic.