Guarm puts 3 foam debuffs on random raiders with something like 8 seconds duration. When dispelled, it jumps to the nearest player, but debuff duration stays what it was – so you have to handle it in those 8 seconds.
When debuff timer runs out, you get a debuff as if you stood in a similar color breath. Point is – if foam color differs from the breath you're soaking you need to go near the person with a correct breath debuff and ask for dispel, so it runs out on him without mixing colors.
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For our Guarm kill we used an addon Nameplate auras, configured to show foam and breath debuffs over the players.
Pros:
You're able to see people and their colors in real-time, so you're not pinned to a certain marks on the floor. And you just hug the nearest raider with a correct color and ask for dispel.
This makes handling the foams much easier.
We also used weakaura –
https://wago.io/4kd1sd-Mz – which assigns each healer to a person with debuff, so you just need to shout your nickname and corresponding healer does that instantly.
Cons:
Make everyone in your raid install the add-on.
You can watch it in action here –
https://www.youtube.com/watch?v=bZbLm3qHGIk