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(You Can) Call on Me is a side mission from South Park: The Fractured But Whole.
Following the defeat of Professor Chaos, The New Kid is contacted by Call Girl (as Wendy) after school, asking The New Kid to meet her in the "appropriate" bathroom at the playground. When they meet up, Call Girl reiterates her suspicions that something is driving the adults of South Park to act increasingly irrational (even for them), but the other heroes are too busy with their feud to pay attention. Call Girl was scouring social media in an effort to find a lead when her phone died; she asks The New Kid to help her get her phone fixed at D-Mobile, claiming that they're "the only one who understands".
This mission becomes available after completing The Hundred Hands of Chaos. After Call Girl, in Wendy's identity, calls you, head to the playground and look for her in one of the bathrooms - if you're having trouble finding her, you may need to talk with Mr. Mackey at the school and change your gender. Once you meet Call Girl, talk with her, then follow her to D-Mobile.
Battle: Crab Peoples and King Crab
Head inside and watch a cutscene before entering a battle with the Crab People. They can stab a hero to inflict Bleeding and spit blobs of goo to inflict Slow; take them on one at a time. Call Girl's Phone Destroyer is an effective counter to their Slowing antics, as its massive range lets her hit them even from across the arena.
When one of the Crab People falls, the Manager King Crab will appear, blowing the heroes across the battlefield with his staff. He'll mostly summon Crab People reinforcements (notably weaker than the first two), but he'll also blast heroes away if they get too close; once again, Call Girl's Phone Destroyer is an effective means of keeping up the damage. Focus all your attacks on Manager King Crab - if he falls, the fight is over - but take out some of the minions if the damage of their attacks starts adding up.
Defeat the King Crab to receive Subdermal Mutation DNA and the Call Girl Character Sheet. You will also be able to selfie with the employees - note that one of them won't accept unless you buy a data plan for 30 dollars.
Boss Fight Video
- If the New Kid is a girl, Call Girl will give her a special artifact: Chromatic Charm during the mission, to get the artifact, the New Kid would have to talk to her at the park after leaving the bathroom.