Gears 3 and 4 had challenges that would pop up during certain waves. Stuff like “execute X enemies” or “get x headshot kills.” If the team succeeded, they’d get a supply drop. They weren’t very worthwhile, but the idea was kinda neat. I think Gears 5 has mechanisms in place to make it a more fun mechanic, though.
Here’s how I picture it: on certain waves, everyone gets the option to play the next wave with an additional mutator. For example, maybe the enemies will benefit from a(nother) More Health mutator, or the Shock Rifle Drone mutator. Only the players who agree to the challenge will have to contend with the mutator, though, similar to how players can play Campaign together on different difficulties. If you agree to the challenge, and make it through the next wave with the additional mutator without dying, you earn a charge of a positive mutator you can use whenever you like. For example, you could earn the ability to have Automatic Active Reload for a duration, or to add ice damage to your attacks. They’d be activated by pressing the Ultimate button with the Tac-Com open. I think this would be a neat way to add variety to Horde, especially the 50-wave variant.