Step 1: Aquire all first 3 relics and load into cursed.
Step: 2: Reach round 40 and have a doppleghast spawn
Step3: Launch the doppleghast on a launchpad (I went from Farm to Janus Tower)
Step 4: Go to Zarya Cosmodrome near the launch site (see cross hairs in screenshot) portal spawns there.
5 Waves total 3 of just killing zombies and 2 HVT rounds.
Challenge: Just don't mark any purchases.
Relice & Effect "Players can only carry 4 Perk-a-Colas