Turning a deadline into a zombie that physically walks toward you is such a simple idea and it actually works - I found myself checking the app just to see how close things had gotten, which is more than I can say for any list-based planner. The weekly/monthly views and recurring tasks make it usable as a real planner, not just a gimmick, and the small bestiary/progression stuff stays light enough that it doesn't turn into a grind on top of your actual to-do list.
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Dial
The zombie-distance framing is a genuinely fun way to make a deadline feel physical instead of just a date on a list. On the game-vs-productivity balance you're unsure about - I'd lean toward keeping the punishment side (the walking, the dread) but keeping the reward side light. The moment killing a zombie turns into a real progression grind (loot, XP curves, etc.) is usually the moment a task app stops being about the tasks. Right now it sounds like you're still on the right side of that line. Are the "different environments" purely cosmetic, or do they change how the zombies behave?