These arent actually undead (though they look like it)
http://www.enworld.org/cc/converted/...and_zombie.htm
It'd make a great mission taking on the creeper(s). They do intelligence drain the spores.. when you hit 0 int you become a yellow musk zombie.
Graphics wise you'd just use the various zombie models or skeleton models, skinned with pustulent yellow flowers, cancerous vegetation growth blob adds.
A mission where you need to lead some travellers/merchants through a yellow musk infested area would be great, where they'd get infested and attack the party.
They count as plant creatures as they're moving by way of the yellow musk creeper which inflitrates the old skeleton.
Seems to be the "morug" skeleton that has flesh within it could also be made this way with "meaty bites" blob adds.