Lo and Li, Royal Advisors Lo and Li, Royal Advisors are mill on demand, very similar to Oona, Queen of the Fae
As you achieve minor weekly quests, such as inflicting X amount of damage or casting X number of spells of a certain color, you earn in-game gold that can be spent on slowly acquiring more booster packs, which you can open to earn a handful of randomly-generated cards
Leonardo Modular, anyone
There's the Field Notes cards (first introduced in Bloomburrow ), along with Power Poses inspired by the show's opening theme
This never answers anything permanently (except tokens), but its pretty hard for things to go wrong with Master Xande on deck
In some cases, you can use Sinkhole to destroy a site, set your opponent back, and if your opponent isnt careful with where they cast their minions, you can follow up with Cave-In , Stormy Seas , or Earthquake to remove multiple cards from the realm devastating your opponents board while setting them further behind in board presence