Once the game becomes day (or less commonly, night), the game will be exactly one of themday or nightgoing back and forth for the rest of the game (barring someone killing the sun with Naturalize 2, I suppose)
Weakness: [metal] x2 Retreat Cost: [Colorless]
A very common way to bestow this wonderful gift to an opponent is with Zedruu the Greathearted
I also think adding replacement and redundancy commanders such as Sythis, Harvests Hand and Calix, Guided by Fate feel like a boring cop-out, especially if you already have other enchantment-matter decks
Starseer Mentor's ability cares whether you gained or lost life this turn, not how your life total changed
Take a look at MaRos articles describing new sets - he does not just dump the image gallery and say let me know what you think - he describes the sets design goals, the mechanics, why they were chosen, how those mechanics were placed in each colour, the limited archetypes the set was designed around, some anecdotes about the design process, etc