This is my second suggestion focussing on the men on Dunland, my previous suggestion can be found here.
So, Berserkers, they're pretty cool and strong guys, and I think the mod nailed them pretty good, there are just 2 things I think that could be improved. The first being this.The second being that Berserkers in real life Used well, oretty much just drugs, these drugs were often made my combining Mead and the Amanita Muscaria. This brew would most likely make them enraged and unsensitive to pain as long as this drug lasted, now let's move on to the suggestion itself!
Berserkers Mead Crafting
This would be a brew only used by dunlendings and either be brewe or crafted in the repective crafting table. If it were to be brewed it would use either the normal red mushrooms, or a special mushroom only found in dunland (I think the already existing one is good). Besides one red mushroom it would just follow the normal mead recipe, so 5 sugar and 3 water buckets.
If it were to be crafted on a table (which I probably prefer) it would use 1 mead, and 1 red mushroom.
The reason I favour the crafting one is that the mushroom would give you the same effects the whole time probably, and it would make it so only evil users could get it easily.
Effects of the Mead
The effects of the mead would be Strength (the rage mentioned above) Resistance (the insensitivity mentioned above) and in general I think it would gove you an adrenaline boost so possibly speed.
And throughout how long all the effects work your screen will be a redish colours and a bit blurred (shoutout to an unregistred wikia user below), this effect would also start a second or 3 before the other effects get applied.
Ech effect would last about 2-3 minutes if crafted, but if you'd brew it it would be 20 seconds with weak, 40 seconds with light, 1:20 minutes with moderate, 2 minutes with strong and finally, 3 minutes with potent. It would also give the nausea given by mead but then much weaker, just going up to 10% or something. And, as said by Lego, some sort of tunnelvision, because I don't think you could see very well with what's technically a drug.
When the mead starts wearing off you'll be granted a slight nausea effect (last 5 seconds or so).
The achievement by drinking this would be [Berserker] and it ould also grant a title called Berserker
When you've killed your first foe using this drink it would give the achievement
Maybe there could be an option of eating this mushroom raw but maybe it would give poison then.
This was my suggestion, hope you like it, and don't forget to check the suggestion that I linked in this one too!
EDIT: For clarification, I don't know much about mushrooms and fungae and how they work, and this seemed an easy way that kidn of made sense to me to do things.