Its keeping a powerful and staple mythic cheaper than it otherwise would be
Thats a very powerful mechanic, especially to noncreature-based decks that are particularly weak to parity being broken in that way
That might be Luminarch Aspirant or Innkeeper's Talent just spicing up your Cube deck with some extra power, or it could be a dedicated build-around seeking to exploit Winding Constrictor and Ezuri, Claw of Progress
Illustrated by Lindsey Look Standard Legal Alchemy Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
In other words, it got to a point where as soon as an Alrund's Epiphany resolved, the game was basically over
He powers up every Spider you have, giving them the same keywords, and that applies to Spider heroes, too