Ultimate IWIN button finally perfected (Elemental Shaman EM+Trink+FS+LvB)

[asonimie]

What does this mean? I've tried /assist focus, even /assist name - doesn't work.

It means that's where your assist system goes. When focus for the macro hasn't been declared yet, it will rely on good old /assist system targeting to pick a target - just like any other multiboxed spellcast..
Different types of Follow/Assist control setups, and corresponding macro example:

Group leader setup (/assist party1),
Specific toon leader setup (/assist Frank),
FTL system (/assist [mod:ctrl,nomod:alt,nomod:shift] Toon1; [mod:ctrl,mod:alt,nomod:shift] Toon2; [mod:ctrl,mod:shift,nomod:alt] Toon3)
Focus Leader System: (/assist focus)

If you are using a focus leader setup... then half this thread will be unusable to you(focus needs to be available for targeting), and for arena purposes I would recommend going group leader or specific toon leader before using focus leader. If you are confused what I'm talking about, then this thread is honestly over your head and you need to read more on introductory multiboxing setup.

Hope this helps.