Planeswalker Nissas +1 offers a steady stream of card advantage/ramp and a somewhat menacing -7 ultimate
Thassa's Rebuff can be a cheaper counterspell for you, although its less effective earlier in the game unless youre countering someone who has tapped out
When cycled, this will give all creatures -2/-2 until the end of the turn, which is a great way to get rid of mana dorks or fodder your opponent might have at a cheaper cost
If you don't want your early game mana-generating land to stick around in your late game, Gemstone Mine is a great option that can sacrifice itself
Warrant / Warden Warrant // Warden is a threat and answer in a single card
That little buddy is named Himoto, also known as Pompon thanks to Kaito, and is the Kami of the Spark, though their origins are pretty mysterious