In fact, a lot of removal spells are bad against this build except specifically when it comes to interacting with your combo, such that there will be awkward tension for opponents when trying to sideboard against you
There will also be two more in-universe sets before that in Tarkir: Dragontsorm and the space-themed Edge of Eternities
and Mightform Harmonizer, which can turn anything into a game-ending threat
There are plenty of RG+ commanders that could make use of the cost reduction on their activated abilities, even if you never pump up Agathas power
For 1 mana, and at instant speed, you can search for any creature in your library and immediately put it into your graveyard, then follow with a reanimation spell
Card 14 will always be either a foil showcase (for Midnight Hunt, the Equinox style) or borderless common or uncommon