So killing Sly Dragon is quite an unique thing in Crimson Peak instance so we would expect a good reward yes? Well since this is an official style server with some bells and whistles, the reward of 2 Dragon Muscle doesn't do much or impact us as it might have on official server. So I would like to suggest buffing the reward a little.
My suggestion would be something like 15 Ancient coin, 3 TPP, 3 Bronze sigils? Could be less or more but this is what i would suggest. Maybe there is a better or a more unique reward to give just post it here :)
Edit: What about like 50-100+ HG or STJ since those are what people are after? Still open for suggestions or tweaks