Do bonuses multiply?
 

Hello,
if I have two things for speed, for example, is the effect multiplied or not?
Thanks ;)

I believe you can have one buff per item, spell, and song. So therefor 3. If your item gives you 20% haste, a spell gives you 20% haste, and bard song gives you 20% haste, you have a total of 60% haste. However, if you have 2 items with haste, only the highest works.

P.S. I'm not 100% on this.

Haste Guide on the wiki may help with some of the specifics

Are you talking about runspeed? Runspeed buffs don't stack. You can have two or more at a time, but only the fastest one takes effect.

Also note that being snared will overwrite SoW or JBoots; and currently, being rooted will also overwrite SoW or JBoots, as root and snare don't stack until Velious.