Are they random? I was doing campaign mode and there's this level where all the enemy worms spawn high above you and rain grenades on your team. Meanwhile you get like all these ninja ropes but very few other means to get height advantage. Needless to say, I've found this level rather difficult to defeat because the Ninja Ropes are damn near impossible to properly control and the combination of high ground and an A.I. that never fucking misses with grenades is simply too much bullshitty for me to handle at once.