whatever i do i can't beat demon 1v1
Just like in normal maze TDs. Making long mazes is usually bait (unless you're abusing some kind of money over time strat). You make one just long enough that your "kill zone" towers have mazing inside their full range. Any mazing beyond that doesn't actually do anything but waste money. Then dump all money into making that "kill zone" as strong as possible. By upgrading the units inside it (Damage>Armor>Health>>Aura). 2-3 of each type inside a single aura towers range will outscale the AI. About 2½ lanes of towers is enough for almost full kill zone saturation.
I beat it using the literal worst possible unit, that's countered by demon armor, doing that.