Scaretiller or Endless Atlas are easy replacements for any of these cards
Like most Magic: The Gathering cards, the value of Soul of Theros depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Magic 2015)
Like many Simic Commanders, " Tidus, Yuna's Guardian" focuses on proliferation and counters
(You'll need to wait to see all the cards and the complete scene they create.) There are stand-alone borderless cards, too, such as those historical figures from games
However, we were given hints on how the set will play, including two of the main themes: legendary-matters, and Food tokens
If its anything other than a character, it gets put to the bottom of the deck, otherwise it goes into its owners hand