They give up entanglement and snare and most of their wilderness skill set is useless outside the desert. In comparison to marshdweller, whose environment is similar in limitation, a lot of their skills are usuable/useful outside their environment. Here are a few ideas on what that skill could be

Suggested skill(s)/spell(s):

Scorpion strike - they put some strong scorpion poison on the tip of a bladed weapon and strike down with a powerful thrust

Quicksand - a more limited version of the spell that's hard to move through and will slowly drain moves if you don't get out, can be used in deserts (but not where a Scion has tainted the ground) to full effect, outside of deserts to a much more limited effect.