Mark Rosewater explains the new colorless mana symbol in detail in "A Solemn Oath, Part 1." So, when deck building, you will want to make sure to support any colorless cards you play
In the early days, Elsa Spirit of Winter was a staple in this deck strategy
And a lot of equipment decks are both using Mask of Memory and also capable of exceeding hand size plus having to discard at the end of turn
For any card printed since 1998, you have two clear indicators: The Set Symbol Color: The most immediate visual cue is the expansion symbol, located on the right side of the card, between the art and the text box
This thing is surprisingly affordable
She is strong in most situations and absolutely lethal against decks like Amber/Steel that rely heavily on exerting characters to sing for the win