As of August 2021, you can STILL obtain both infection-related achievements:
- Delicious Brains - On a Mythic map, infected 2 humans during a ranked or social match.
- Zombie Repeller - On a Mythic map, killed 2 Zombies during a ranked or social match.
Rumble pit is
currently broken via playlist selection, but the infection game mode "Mmm...Braiiins" can be found on the
7 on 7 playlist. My session group went in with 7 individual players, but you can have extra controllers for guests or at least a few players to start the matchmaking search.
The Mythic maps are as listed; Be sure to pay attention to the pictures because map variants still count!:
1. Assembly - Dismemberment (variant)
2. Orbital - Andromeda (variant)
3. Sandbox - Spooky House (variant)
4. Longshore - Dead Docks (variant)
5. Heretic
6. Citadel
HOW-TO GET ACHIEVEMENT*** Spoiler - click to reveal ***After finding the right playlist (will show the biohazard symbol for an infection/zombies gametype) and mythic map/variant. Have the shotgun players kill the infected first for the Zombie Repeller achievement. Then methodically, have infected players kill 2 shotgun players each for the Delicious Brains achievement. You should get several rounds of the game so if someone missed it, you can get it in the next round. WARNING: It may glitch the kills like it did for me, where I killed 2 survivors, but it didn't unlock the achievement, but I was able to get it in the second round.
It took awhile hours to finally find the "Mmm... Braiiins" playlist on the CORRECT map (ours ended up being a map variant of Assembly). If it isn't on any of the maps listed, you'll have to search again until it rotates to the right map. We got the right playlist 2 searches in, but it was on a base map so it didn't unlock achievements. GLHF!
EDIT:
As of August 30th 2021, the Rumble Pit Playlist is working again! I saw several Braiiins playlist on different infection maps so go for it!