If you're a prowess sort of spell slinger deck, you want your threats to be cheap so you can cast them early and then start chaining together a bunch of spells
Frequently Asked Questions How much is Akroma's Will worth
And when we say cheap, generally most people are equating prices below $50 to be super cheap for a deck
Non-Starting Player (You) - At the beginning of your turn you draw a card, then proceed to place a card into your Inkwell
I could also see Sarkhan being the key piece of a R/B Control deck which is the kind of deck that always looks better on paper than how it performs because of the variance in its draw steps and lack of velocity to filter through the deck, the exact problem Sarkhan can solve
Phyrexian mana on the ability, while being very flavorful, is also great mechanically, and its just really neat all round