SC2Mapster

Is there a way to make a requirement that only permits 1 Hero at a time. When trying to buy new ones.

I can only find ways to do it with specific units such as the mothership requirement. Can't find unit attributes?

Well in fact is the same what you want, only be able to have one hero at a time, so the Mothership requirements fits that. Only edit the Level's name to fit your hero's name and done.

use hidden custom resource, -1 for unit cost and trigger +1 on death

Quote from TheSC2Maniac: Go

Well in fact is the same what you want, only be able to have one hero at a time, so the Mothership requirements fits that. Only edit the Level's name to fit your hero's name and done.

What if I have 20+ heroes?

Well, the straight forward way would be (Sum of (Hero 1 + Hero 2 + ... + Hero 20) < 1). But to avoid listing every single hero here, you could go for a workaround, like Disturbed suggested for example.

You could also tinker with the unit's Tech Alias, so all the heroes count as the same unit for the requirement, but I am not sure, if it will work well; it might interfere with other stuff, depending on your map.