Giving purpose
Very quick, (for example after reaching level 25), I feel a lack of purpose. Ending was great at making you wish to reach level 8.
I don't know what you make the player wish to keep playing (and staying faithfull to the name "Unending"). Maybe through counting (a displaying on a screen) the number of creature combinations the player has met, or interracted with (bumped into, pushed, switched placed or killed).
When the player reaches increasinlgy larges numbers of different creatures, he could be rewarded with something (a random text ?).
And it would turn the player into a hunter. (I want to catch that bullet ! I want to make that encased explosive and hooked arrow multiplayer explode...)