With a mana value of 3, which triggers Yshtolas damage ping to opponents and healing for you, this Enchantment-Aura card has Flash, meaning it can be played with the speed of an Instant
A severe exploit in this manner is unlikely, however, given the lessons WoTC has already learned from older abusable counter-based cards in MTG
The situation with the day/night imbalance very likely has to do with its Eldrazi prisoner
Being the only game in town for no-art lands would make Unstable more similar to Unhinged or Unglued , where if you wanted a certain subgroup of basics for your deck, you pretty much had to buy the set (or at least the lands from the set, which would force someone else to crack a box of the set to sell them to you)
If this spell was cast from a graveyard, instead create X of those tokens, where X is the number of creature cards in your graveyard.Flashback (You may cast this card from your graveyard for its flashback cost
Like previous bundles, you get 40 basic land cards, a spindown life counter and a foil alternative-art card