Creeping Doom is another one that adds a little slow effect. I enjoy it as they help the spells do a bit more damage to charging onslaughts of enemies. (or allies!
) Grovel's been having quite some fun with Creeping Doom lately... the gobbo-wolf now has attack fleas!
The movement rate reduction for cloud and swarm spells is likely due to the victim coughing, itching, burning, gagging, etc. Web too has a slowing effect to those in the area, though it notes this in that particular spell description. This one and other spells that reduce movement rate might have their Lore descriptions updated as well.
-Cloudkill
-Creeping Doom
-Horrid Wilting
Now that you mention it, I'll keep an eye on any other spells that have movement rate reduction effects not noted in their description and make a post to the LORE Suggestions/Bug Reports when I'm satisfied experimenting on Nonac.