I think that's a lot of makework - of course that's what this game is all about
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If you want to implement tokens, I think the best way is simply to give them out to raid leaders with a certain limited frequency (2 per week sounds about right). If you successfully kill said raid mob within one hour, you get your token back one week later. Otherwise it despawns and you don't get your token back for a month or so. All the ordinary boss mob pops would work as normal. It does seem like a reasonable balance between instancing and competition, although I don't know if I like the idea of guilds getting to spawn personalized raid mobs.