jgsugden
Legend
The PCs placed the rope. The PCs climbed the rope. All the goblin (which was following them) did was cut it as they climbed.I think the goblin cutting the rope would count as a trap which the OP ruled out?
By definition, the CR system should indicate that you should not be at reasonable risk of a TPK unless there are unusual environmental considerations. If you put aside unbalanced creatures like pixies, then some form of physical assistance is required.
However, if you want a neutral battlefield, your best bet is a few pixies.