If you don't have blink at the start of this level at 2, your going to be annoyed. You have to then climb up pretty high. Make your way through some small tunnels eventually to a porch uptop with a door. Iniside there is also a wall of light and a ton of guards.
After that it gets down hill. Dodge a tall boy and keep blinking towards the target.
Once inside regents safe area, you should kill the Lord regent face. Blink past the tall boy and assainste the regent. If he flees your going to have to find a key, so better to restart mission and just kill him, then everything else. Finally if you want to collect everything continue item hunting from that point.