Hey, I'm not the dev, but just looking through the code what I gathered was:

1. The Berserker Charge tactic is dependent on both a. having a North Germanic culture commander commanding the flank, and b. at least 1% Heavy Infantry in the flank. It gives a x4 bonus to Berserker attack with no defense debuff, which makes it especially powerful.

2. Berserkers appear to be viable, so long as you can suck up some losses in the skirmish phase and never plan on routing. Compared to Heavy Infantry, they get -40% skirmish attack, +33% melee attack, +200% pursue attack, -50% skirmish defense, equal melee defense, -75% pursue defense.

3. Berserkers are under Heavy Infantry.

4. They are not required to trigger any tactics, but they do get buffed / debuffed by preexisting tactics. Some that stood out to me were:

Skirmish phase:
Shieldwall - usually you want to trigger this when using Heavy Infantry. Don't. This tactic makes Berserkers cry. They get an additional -50% defense with no bonus to attack. If you plan on using Berserkers, never mix in Archers.
Charge - no requirements to trigger, aside from 10 days into skirmish. Immediately sets the phase to melee and gives Berserkers +350% attack. Heavy Infantry get +120%.

Melee phase:
Advance - needs 1% Heavy Infantry to trigger. Gives +300% attack to both Berserkers and Heavy Infantry. Gives another +300% against enemies using Stand Fast class tactics. Beware charging enemies.
Berserker Charge - needs 1% Heavy Infantry to trigger. Gives +400% attack to Berserkers but only +360% attack and -50% defense for Heavy Infantry. Gives an additional +100% bonus against enemies using Advance class tactics. Beware enemies standing fast.

@el_nora: Thanks for answering. Somehow I don't get notifications when new discussions are opened.

Will the berserker get a unit model or at least find a way to set to a different model cuz it shows upas a genric archer unit

I'm not a 3d artist so making an entirely new model is kind of out of the question. One could use the heavy infantry model I guess. I'll have to take a look how thats done.

cool it was just a thought !