First of all, that you can ease the mana base a bit, and you will never have problems needing colored mana of any kind
All you have to do is tap on the card in question and choose "obtain flair," which will then show you how many duplicates of that card you need
While only affecting a single creature type restricts Cavern, typal decks can leverage this to ensure their threats get through countermagic, be they efficient merfolk, monstrous dinosaurs, or sneaky goblins
The blue in the deck is a very light touch, dipping into the Blue-Black zombies from Amonkhet (Gleaming Overseer, Spark Reaper) and Innistrad (Havengul Lich, Diregraf Captain, Champion of the Perished), as well as a handful of counterspells (Sinister Sabotage, Undermine) and card draw (Distant Melody, Deep Analysis)
At the beginning of your opponents end step, they may tap any number of untapped creatures they control with total power 8 or greater
limited event costs the same as an Arena booster at 200 gems or 1,000 gold