The campaign difficulty level is kinda mixed up - lvl1 chars shouldn't be able to survive tadpoles, let alone escape from hell!
Tadpoles works the same regardless of your level and these are special.
As for escaping from hell, I died in the intro twice. First time, the Cambion Commander killed the Mindflayer super quick and one-shot Lae'zel and then me on his next turn. The second time, the Cambion Commander get killed by the Mindflyer who then decide to kill me while I was dealing with the imps.
My biggest success has been to use dash every turn and use the transponder as fast as possible...and not fight anything.