MarsSeed [1] filed a deletion request for zenity-gtk2 [2]: Doesn't build in a clean chroot. Not useful to keep. There is no pure- Gtk2 desktop environment available from Arch or AUR repo. Users should stick to Arch repo's zenity.
[1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/zenity-gtk2/
