The systemd 188 merge has left a few packages that must be manually removed before
a successful system upgrade can be performed. This command should help you if you
are encountering this problem in current:

pacman-g2 -R systemd-gtk systemd-plymouth dracut-plymouth plymouth plymouth-theme-frugalware plymouth-theme-glow plymouth-theme-solar plymouth-theme-spinfinity

After this command you can upgrade by proceeding as you would normally. Thank you.