You can use it for artifact abilities like Clues and Foods, or something entirely different like exhaust costs or pump abilities
However, the increase in price from the beginning of the month to today is rather significant
Chief - NCC: Bennie Bracks, Zoologist: Bennie Bracks looks like he would get along great with the aforementioned Rumor Gatherer, as theyre both mono-white elves with a passion for zoology and drawing cards
At any rate, each time you cast Gandalf the Grey you get to use the full bag of tricks again, and you can also blink the card to reset it
The Poliwag is common, it'll probably only get around .10-.25 cents
Where Grist really becomes overpowered is when used in combination with cards like Forever Young, which lets you put any number of creatures from the top of your deck into your graveyard