When discussing mana in print, the convention is to use letters in order to reflect which symbols we are talking about when we aren't able to just use the symbols
Commanders cards like Tezzeret, Master of the Bridge and Armix, Filigree Thrasher need your mana support from a card like Mistvault Bridge
Black-green is one of my favorite color combos to begin with, and Eldraine is full of fun cards like Bake into a Pie, a black instant that destroys a target creature and bakes them into a Food token, Sweeney Todd-style
There's two reasons for this: The more spells you spells you cast with K'rrik's discount, the more powerful he is in your deck
(They're artifacts with ", Sacrifice this token: Add one mana of any color.") You might also be interested in these products
A Magic: The Gathering collection often consists of a combination of the factors mentioned above