My system froze during a kernel update. I was downloading a big file at the same time, so I think I ran out of ram. I couldn't access tty, so I just forced reboot with powerbutton. As one might expect, system could not boot normally after an interrupted kernel update.
Normally I would boot an iso from grub, chroot in, update, regenerate initcpio and update grub. But I have Timeshift-autosnap installed, so it was even easier to fix: I chose snapshot from 2 minutes ago from grub and booted into it. Opened timeshift and after two clicks my system was restored and I could reboot normally.