One of my players is a druid who would like to be able to change their creature type so that they become an invalid target against spells that target humanoids. First party WotC content (including UA) is preferred, though items from previous editions are also acceptable that can be supported by gameplay in 5e.
The option for using their wildshape to turn into a Beast is an obvious option, as is using spells like polymorph, but I'm looking for mechanics beyond those.
A spell scroll of Nystul's Mystical Aura in D&D5e is the closest I've found so far by allowing the target's creature type to be changed for divination spells, but the target is still physically its original type and may still be valid against spells targeting humanoids. Changing to a plant creature type would be ideal in this situation to further some roleplaying aims, though some "minor" bookkeeping changes like vulnerability to fire are also okay.