Two of the rewards tied to the starting house in Rex Infernus share the same rule. You have to stay inside. The Goat Mask hides behind a painting on the first floor, and the “TUTUS MORTUORUM” Dark Ops challenge asks you to survive deep into a run without ever stepping out. Both are doable in a single sitting if you plan your Gobblegums and hold the right spot.
Quick answer: To grab the Goat Mask, survive the first 10 rounds entirely inside Her House, then melee the painting on the first floor at the start of Round 11 and pick up the mask that appears. To complete Tutus Mortuorum, keep going without leaving the house until Round 30 ends and the game flips to Round 31.
What the Goat Mask does
The Goat Mask is a wearable with a passive effect. When you stand still, a purple ring of fire forms on the ground around you. Zombies that walk into the ring take damage and get weakened, and your own damage output goes up while it is active. It behaves like the Ring of Fire mechanic from older Zombies maps, right down to the trade-off. The effect only triggers while you hold position, it lasts a few seconds, and it goes on cooldown after each activation.
That makes it strong for locking down a doorway or catching your breath at the end of a round, and far less useful when you need to keep moving through a busy horde.
How to unlock the Goat Mask in Rex Infernus
The whole process happens inside Her House, the building where every run starts. Before you commit, set a Gobblegum loadout built for survival, because you will not be visiting the wider map for perks or ammo.
Note: The same painting can drop randomized loot on other rounds if you keep punching it while you hold out, so do not be thrown off if a weapon or tool appears before the mask. The mask itself is the reward tied to staying long enough and hitting the painting on Round 11.
Tutus Mortuorum Dark Ops requirements and reward
The challenge card reads “COMPLETE ROUND 30 WITHOUT LEAVING THE SAFEHOUSE ON REX INFERNUS.” In practice that means surviving until Round 30 finishes and Round 31 begins, all while confined to Her House. Answering the phone teleports you to the Nexus Forge, which counts as leaving, so skip it for the entire run.
| Detail | Value |
|---|---|
| Challenge name | TUTUS MORTUORUM |
| Condition | Reach the end of Round 30 without leaving the safehouse |
| Reward | Dark Ops calling card and 15,000 XP |
| Extra | A new Exfil becomes available on completion |
Since the Goat Mask unlocks at Round 11 in the same location, you can equip the mask and then keep pushing toward Round 31 in one continuous run.
Survival setup for reaching Round 31
Her House has no ammo boxes, so your Gobblegums carry the run. Lean on packs that hand you perks, armor, ammo, and weapon upgrades without needing the rest of the map.
| Gobblegum | Why it helps |
|---|---|
| Perkaholic | Grants all perks at once, covering PhD Slider and the rest without machines |
| Armor Up | Restores armor when you have no reliable buy station |
| Wall Power | Buys and upgrades the Coda 9 wall weapon |
| Fully Packed | Upgrades a Mystery Box weapon straight to Tier 3 Pack-a-Punch |
| Flavor Hex, Crate Power, Wonderbar | Improve your odds of pulling an upgraded Ray Gun from the box |
The house does have a Der Wunderfizz Gobblegum machine and a Mystery Box, so you are not completely without resources. A Ray Gun from the box, ideally upgraded, is a strong crowd-clearer for the later rounds.
Weapon and positioning
Use Wall Power to buy the Coda 9 off the wall for 500 essence, which gives you an upgraded pistol without needing an ammo box. It fills the gap between Mystery Box pulls and keeps you topped up on rounds where ammo would otherwise run dry.
For holding rounds, set up in the stairwell. Zombies only push in from the front there, which turns a chaotic multi-side defense into a single lane you can control. Molotovs, Toxic Growth near your camp spot, and the Ray Gun cover the rest. The spider elite does not spawn inside the house, so you only deal with standard zombies and spider rounds all the way to Round 30.
How to confirm it worked, and what breaks it
For the mask, the confirmation is visual. The painting opens after your melee and the Goat Mask sits behind it, ready to pick up. Once equipped, stand still and watch for the purple ring on the ground to verify the effect is live.
For the Dark Ops, you will see the “TUTUS MORTUORUM” unlock notification the moment Round 30 flips to Round 31, along with the 15,000 XP payout and a “NEW EXFIL AVAILABLE” prompt.
The most common way to fail is leaving the house. Answering the phone sends you to the Nexus Forge and voids the no-exit condition, and so does opening a door to step outside. Because there are no ammo boxes indoors, the other failure point is simply running dry. Keep Wall Power and a box weapon in rotation so you never stall on ammo before Round 31.
