It pays to watch monsters before teleporting. If their path takes them across obstacles that change the way they face, you may need to time your teleports around this behaviour.
Poison gas will kill Yuri if he teleports into it, but monsters will be fine. If you see a wavy green area in a level, don't teleport Yuri into it.
Some monsters will kill each other if you let them run into each other. You'll need to juggle teleporting Yuri and them if they're all in the same area together.