The inclusion of deathtouch and haste is nice, but Mardu Siegebreaker still needs to potentially put itself in harms way in order to do its thing
Ultros gives you a great way for those kinds of spells to interact with your opponents creatures and slow them down, giving you more time to cast awesome spells
Spider-Man, Brooklyn Visionary Spider-Man, Brooklyn Visionary is probably one of the best legendary common cards in Marvels Spider-Man
Crashing Footfalls, Elementals, and Bring to Light Scapeshift all have few turn one plays, so they can stand to fetch a Triome on turn one and start setting up their mana
Clunky hands: How often are you forced to keep slow hands because you cannot mulligan forever
Obviously it's no Mox or Black Lotus, but as we noted at the start, this list would be really boring if we just went through the Power Nine