Item slows do not stack with each other (they are a special slow type). This includes Phage, Trinity Force, Frozen Mallet, and Rylai's Crystal Scepter. Warden's Mail and Randuin's Omen do stack with other item slows (but again not with themselves from the same person).
Most slows will stack if two different people use them (for example double Exhaust) but item slows are an exception, they are limited to the biggest single item slow, from any player.
I suggest you make your voice heard on the LoL boards in favor of greater transparency in LoL game mechanics. I shouldn't have to test mechanics in practice games to figure out how they work, and neither should you. Yet here I stand with a great breath of mechanics knowledge for no other reason than the fact that I spent hours playing practice games to test stuff. The game wasn't created so people could go on and test stupid crap... it was made to be played and enjoyed. I should also be able to trust that the information communicated to me in STICKIED THREADS is accurate.
horray, the stickied thread has finally been corrected. There is one less thing in there that might be wrong...
Fury and Civil Enemy did a great job testing things and posting their results in this thread. Here are some things worth noting:
- Frozen mallet slows for 40% when used by melee champs and for 30% when used by ranged champs.
- Slows stack multiplicatively, not additively.
- Any slowing beyond 220 movespeed is only 50% effective because of diminishing returns coded into this mechanic.
If you want to see specific examples, take a look at this post:
It should help paint a clearer picture for how slows stack.
Changes to slow stacking were made in patch v220.127.116.11 but not noted in the release notes...
We forgot to include a change to slow stacking in the patch notes. I wanted to let you guys know the change;
Diminishing return for slows kicks in at a given number. This means that the first slow you put on someone might have been hitting diminishing returns and slowing for a little less than intended.
The first slow you put on a target always slows for the amount stated. Subsequent slows remain multiplicative, but slows beyond the highest % slow are cut in half (and then applied fully).
General implication: Single slows will be as strong or stronger than before. Multiple slows should be weaker than before.
[Edits to clarify the system]
The largest slow will always take the full effect. If a champion is affected by the slow from Blessing of the Lizard Elder and then walks on Mega-Adhesive from Singed, the Mega-Adhesive will now slow fully and the Lizard slow will be cut in half. If the champion uses Flash to escape Mega-Adhesive, the Lizard slow will now go back to full power.
special thanks to peyo for bringing this to my attention!
Small change to slow mechanics from patch v18.104.22.168