I would slow people who were dueling me to proc their OT hammer. That's when I was exposed to this mechanic. Also I'd use this trick with my Di`zok Oracle Shillelagh to help with the initial slow at raids. Then back off and do Turgur's Insects for max slow.
Nice write up. Could be added to the wiki.
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https://wiki.project1999.com/Weapon_Procs
edit: also enchanter can slow!
https://wiki.project1999.com/Debuff_Guide#Attack_Speed