移し
Not the same form as 創りし or 宿りし
Forgot to add: “移し” is actually not the same form as “創りし” or “宿りし”.
“移し” is a common, modern continuative form ( 連用形 (れんようけい) ) of 移す (うつす), “to transfer”. It is used for example when enumerating activities that directly follow each other. It is created simply by putting the verb in its stem form (polite, without -masu). Here it can be understood as “transfer [the power to this key]” (移し) AND lend it to me!" (tried to emphasize the continuative form - transferring to the key is directly followed by the lending of power). It confused me a great deal too when I stumbled upon it for the first time, reading some folk-tale. 