Use the Wunderbarrage Controller on the Garage Door to gain acccess to the building.
Next, you'll need to obtain three different pieces of Uranium:
Use an Olaf's Cod Cranker to find and fish up a green fish, which will spawn an Irradiated Ravager. Kill it to receive the Uranium.
Use a Glocke Drop and kill 20 zombies while they are in the air to receive the Uranium.
Head to the Core Foundry and melee open the Vent. Send an ARC-XD through the vent and use it to blow up barrels to open the lab underneath the building on Fishery Island. Once inside, note the numbers next to the doors in the hallway with the radiation symbol, then convert those to letters and place the corresponding jars with the letters onto the Jar Machine. Grab the liquid and pour it onto the large arm on the table of the lab to acquire the Necrospike. Use the Necrospike to lockpick the door into the Uranium.
Head to the Claw Machine and place all three uranium inside.
Interact with the Claw Machine and line up the uranium inside so that the perfect amount of energy goes through, then grab the Atomkraft Core.
Place the Atomkraft Core on the pallets near the Generator and defend it until it's charged.
Place the charged Atomkraft Core to the Barrel on the bridge then grab the Dravakar Shard after the cutscene.
Bring the Dravakar Shard to the Fireplace in Blodheim Hall, place it inside, then use the Jotunn Star's secondary attack to light it.
Use a Disciple Injection to grab zombies then throw them into the bonfire.
Kill all the zombies during the lockdown and grab the Sunstone.
Place the Sunstone on the Altar inside the church then use the Jotunn Star's secondary attack on it.
A large rune will appear in the sky with arrows. There will be floating runes around the map. Use the Jotunn Star's secondary attack on the wood under each rune in the order by how many lines are on the arrows pointing to it.
Head into Tyr's head and interact with Tyr to begin the boss fight.
