It helped to take a tribe that is historically more expensive in terms of mana value and recontextualize them to be a little bit faster
If a creature enchanted with an Aura that has umbra armor has indestructible, lethal damage and effects that try to destroy it simply have no effect
The card must be able to be built-around in multiple ways in the format (sorry The Rack, Scapeshift, and Ad Nauseam, you don't count.) At least one deck that uses the card must be Modern viable at the time of this publication Now with only ten spots to use, I know I'll inevitably leave out some favourites, so please don't be shy in the comments with some honorable mentions
Dealing damage in increments of two was seen as leading to a desirable pace of play
If you play a deck that wants to get some beaters down, this can close out the game in no time
Many cards break into the 3-figures if they're not printed enough, like Power Artifact, and its not uncommon to get into 4, 5, and even 6-figure price ranges for the ultra-rare