Help with potion effects! (Need something like "Weakness")

So, I'm making a mod that has a potion effect that slows enemies while also taking some of their attack-damage

One example for the effect is exhaust effect from League of Legends.

The thing is, I'm using the "attributes" plugin and it actually works! But I think I may be doing something wrong with the code, so I would like some help

This is just a test, so bear with me if it's too wrong!
I really need some help with this code, it's a core thing in my mod