Radar skill in Underworld requires pararitic flare gun, can be bought at the ai base where you get the skill. Change it to something else, like Solar Prisms or something.

For Equipment, could change Traginium requirement for a lower level, make hellfire remains for higher level as they are more difficult to obtain

Might be a few other skills, should make things a little more challenging for low level players. Running around with mats for skills at low game stage is a good way to have people go through content.