For a full list of purchasing links by release platform, see the releases page.
As of February 2020 Killer Queen Black is priced at $9.99 in the Nintendo eShop and on Steam. You can buy a 4-pack via Steam for $29.99 as well as a commercial license for Steam Cafe at $59.99.
You can gift Killer Queen Black on steam! See this Steam Support Page for more information.
Unfortunately for Nintendo Switch, there does not currently seem to be a way to gift the game.
If you already own Killer Queen Black on Steam but want to purchase the 4-Pack for friends, you may be prevented by the Steam Store due to already owning one of the copies of included in the 4 Pack.
To get around this purchase the 4 Pack through Humble Bundle, and you will receive 4 individual keys for distribution to your friends, without the Steam Store restriction.
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