The Cripple

Todt zum Krüppel: HIncke auch her mit deiner Krucken, Der Todt wil dich jetzund hinzucken: Du bist der Welt gantz unwerth sehr, Komm auch an meinen Tantz hieher.	Death to The Cripple You too, hobble over here with your crutch;. Death will now snatch you away.(1) You have been wholly unworthy to the world. Come to my dance here, you too.

Der Krüppel: EIn armer Krüppel hie auff Erd, Zu einem Freund ist niemand werth: Der Todt aber wil sein Freund syn, Er nimpt ihn mit dem Reichen hin.	The Cripple. A poor cripple here on Earth. Not worthy of being anybody's friend. But Death will be his friend, he takes him away [along] with the rich.

Klein-Basel, Cripple.
Line drawing after Büchel

Death heartlessly mocks the cripple by imitating his primitive prosthetic leg. Has it been like that since the mural was created around 1440? Or is it a newer element from a later renovation?

That's hard to answer because if we look at the same scene in Klein-Basel, it's impossible to see if the cripple has lost a leg — because the painting is interrupted here by a doorway at the end of the western wall. It's also impossible to tell whether Death has "dropped a leg" owing to the deteriorated condition of the mural.

The dialogue is reminiscent of Heidelberg's dance of death,

Footnotes: (1)

snatch away. . .: The word "hinzucken" is also used in old German Bibles in 1^st Thessalonians 4,17: »darnach wir, die wir leben und uberbleiben, werden zu gleich mit demselbigen hin gezuckt werden in den wolken […]«.
King James renders it as »Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.«.