“Cave here. Just so you know, this mic isn’t two way. Can’t hear a damn thing you’re saying, so don’t waste any oxygen trying to talk. [off mic] What? [on mic] My assistant Greg says some of these alternate Earths may not have oxygen. The air might be nitrogen or methane or, hell, everybody’s head might be inside out. So just take little itty bitty breaths and if anybody asks you why your head’s inside out, remember it’s only inside out from their perspective, and you’re fine. Head-wise. Trouble-wise, you’re in a lot of it and you should probably run. Alright, enough hypotheticals. Let’s test this test!”  
-Cave Johnson. Portal 2. Perpetual Learning Initiative. Datalinks.

When traversing the multiverse, be wary of the other universes around you. If you fail to be cautious, you may find yourself facing down an eldritch abomination that was fantasy in you’re reality, but very real in it’s own.
 
This has been Multiversal Traveling Tips (tm), for all your multiverse traveling needs.