Stealth HELP

I need to make an ability called stealth. It's basically the same thing as windwalk, but it slows down the movement speed instead of speeding it up. I tried putting a negative value into the spell, but it only goes down to 0. I tried using triggers, but it gets too complicated when the unit breaks out of invisibility. Could anyone help me out? Suggestions?

Try holding either Shift or Ctrl while clicking the value, set to a negative value, and hit okay, that "should" work. :)

YES!!! It worked perfectly! thank you tons, now I can finally finish my map.

You can also select "allow negative values" under Preferences.