I think if you need to even up an odd stat, even something like Medium Armour proficiency can be good: you pop your dex by one, and also gain use of shields, giving you a total +3 Amour Class boost.
A handy haversack or bag of holding with just enough water could help. So could an urban campaign, where he can have a bath each day. Someone suggested a level of druid, so he can create water.
Any suggestions about Grung rogue guides? I've looked at a lot of rogue guides on this site, but none address Grung.
I'm using the simple Grung stats from One Grung Above:
Having been intrigued by the Lankhmar kickstarter, but not being familiar with, or wanting to explore, DCC, how difficult is it to convert to 5e? Are there any guides?
According to the 3.5e Manual of the Planes, and the 5e Volo's, Vlaakith has no generation number because she's a lich, and immortal. So the adventure may not be canon.
How about:
"If the damage source is a critical hit or a failed save against a spell that does half damage on a save, the check is made with disadvantage. "