Ancient Blades heropower replaces the Poisoned Blade instead of giving it +1 attack.

[Adusak90]

https://www.youtube.com/watch?v=hjT4CZeUlbQ

There is no "basic" keyword, therefore all heropowers granting weapons should work.

[Jetz72]

https://playhearthstone.com/en-us/blog/23239986/hearthstone-update-december-5-descent-of-dragons

Fixed an issue where Poisoned Blade would get replaced by Ancient Blades instead of getting +1 Attack.

Should test another hero power just to be sure it isn't hard-coded.