The following heroes are no longer restricted from buying Basher: Spirit Breaker, Faceless Void, Slardar, and Troll Warlord. They are still restricted from activating Bash.

Does skull basher stack with Slardar?

Does not stack with other sources of Bash, however it will stack with Mini-Bash. The following heroes cannot trigger Bash on this item: Spirit Breaker, Faceless Void, and Slardar. Dispellable by strong dispels only.

Can Basher buy void?

Yes it is. You cannot buy basher on void, troll, slardar and spirit breaker.