Rex Infernus: How to Get the Corrupted Olympia and TR2 by Round 5

On Rex Infernus, you can walk away with an ultra-rarity corrupted weapon as early as round 5, long before you would normally reach that tier through the Mystery Box or Pack-a-Punch. The two options are the Olympia shotgun and the TR2 marksman rifle, and which one you get depends entirely on the wall buy you purchase first. The catch is that the finished weapon damages you the moment you pick it up, so the whole routine is a race against a health drain.

Quick answer: Buy the Breacher (for the Olympia) or the Novaline (for the TR2), Pack-a-Punch three weapons, trigger rain so the wall buy glows, use the Void Claw to make Astral Fire at Pack-a-Punch, throw that fire at the wall buy to spawn Maldruk, kill it, then grab the Unstable weapon and immediately Pack-a-Punch it to stop the damage-over-time.

Player aims a rifle inside a glowing orange ring in the Nexus Forge with an Open prompt — The Nexus Forge is the central hub where you crank the Pack-a-Punch machine for Astral Fire. Image credit: Treyarch / via @ZoneXbez

Pick your weapon and wall buy

The corrupted weapon you end up with is decided before anything else. Each of the two legacy guns starts life as a specific wall buy, so buy the one that matches the weapon you want.

Corrupted weapon	Wall buy to purchase	Location
Olympia (shotgun)	Breacher	Caltheris Entrance
TR2 (marksman rifle)	Novaline	Dravakar Sanctuary

Aiming at a wall-mounted shotgun pickup beside a glowing blue altar at Caltheris Entrance — The Breacher wall buy sits at Caltheris Entrance and becomes the corrupted Olympia. Image credit: Treyarch / via @ZoneXbez

Full setup, step by step

Buy your chosen wall weapon. Purchase the Breacher at Caltheris Entrance if you want the Olympia, or the Novaline at Dravakar Sanctuary if you want the TR2. This locks in which corrupted weapon you can create.

Pack-a-Punch three weapons at the Nexus Forge. The counter tracks how many upgrades you have done, and you need three before the wall buy will react later. You can cycle the same guns through the machine to reach the total.

Pack-a-Punch Level 1 machine showing INSERT FIRE and a prompt to buy the M34 Novaline upgrade — The Pack-a-Punch machine tracks your three upgrades; here it shows the Novaline path for the TR2. Image credit: Treyarch / via @ZoneXbez

Make it rain on the next round. Turn on the gravity pool in the Aetherium Temple, or simply wait for an ammo round to trigger the weather. Once it is raining, the wall buy you purchased starts glowing.

Return to the glowing wall buy. Confirm the glow is active before moving on, since the next steps only work while it is lit up.

Grab a Void Claw grapple and make Astral Fire. Pull one of the floating orbs into the Pack-a-Punch machine with the grapple, then crank the machine so the energy is absorbed and produces Astral Fire.

Carry the Astral Fire to the glowing wall buy and throw it. This spawns Maldruk, a high-value spider target, at the wall buy location.

Aiming toward a glowing purple doorway at Caltheris Entrance with the Frenzied Guard ability ready — Throwing Astral Fire at the lit wall buy spawns the high-value spider target Maldruk. Image credit: Treyarch / via @ZoneXbez

Kill Maldruk. Once it dies, the wall buy transforms into the Unstable Olympia or the Unstable TR2, depending on your earlier choice.

Grab a Void Claw before you touch the weapon. You will need the grapple to move fast in a moment, so have it ready in hand.

Player moves along a Nexus Forge walkway targeting a labeled Deathspinner enemy — Keep a grapple ready so you can rush back to Pack-a-Punch before the health drain finishes you. Image credit: Treyarch / via @ZoneXbez

Pick up the Unstable weapon and sprint straight to Pack-a-Punch. The weapon drains your health over time the instant you hold it, so use the grapple to cover ground quickly and do not stop to fight.

Pack-a-Punch the Unstable weapon. Upgrading it removes the constant health drain and leaves you with the finished corrupted version.

How the corrupted weapon behaves

After the final Pack-a-Punch, the health drain stops completely. You will know it worked because the “Unstable” label is gone and your health stops ticking down while you hold the gun. From that point, the corrupted weapon only damages you if you fire a shot and miss every zombie. Land your shots and you take no self-damage at all, which makes accuracy the only cost of using it.

Common reasons it fails

Problem	Cause and fix
Wall buy will not react to Astral Fire	It only responds while glowing. Make sure rain is active before you throw the fire.
Astral Fire disappears before you reach the wall buy	The fire is timed. Pull a fresh orb into Pack-a-Punch and crank again, then head straight over.
You die carrying the Unstable weapon	The pickup drains health immediately. Have a Void Claw in hand and go directly to Pack-a-Punch without detours.
Nothing spawns after three upgrades	Confirm you Pack-a-Punched three times and bought the matching wall buy first.

Done cleanly, the entire loop fits inside a single early round, giving you an ultra-rarity gun with almost no downside long before the map would normally hand you that kind of firepower.