Xabre [1] filed a deletion request for mudlet-dev [2]:
Mudlet developers no longer deliver development prereleases, it has
been like that since version 3.0. This AUR package has outserved it's
purpose, users should use either mudlet or mudlet-git.
[1] https://aur.archlinux.org/account/Xabre/
[2] https://aur.archlinux.org/pkgbase/mudlet-dev/