This achievement is only available through FFA playlists as of the July 20, 2023 update. Any suggestions prior to that date likely won't work as the makeup of this achievement has changed since then.
After capturing 10 skulls multiple times in 4v4 Social Games and still not getting the achievement or medal, I used the method
Sp4rrkz listed in his solution for clearing local saved data from your console (again, NOT from everywhere). This also did not work for me. That could still be an issue for you, but ensure you follow the explanation below first before clearing your local saved data.
Explanation:Since the update, the Skullamanjaro
medal is strictly tied to "instant wins" which is the legacy setup. Instant wins can be enabled in custom games through the "specific game options," but in matchmaking, it is only preset to be ON for the FFA playlists, not team games such as 4v4. To get the achievement, you need to get the medal. This achievement is for matchmade games, not custom. Therefore, Social Games FFA is your only option.
You can still do this by searching a custom matchmade lobby. I searched:
- Social Games
- 8 Player (FAA)
- Halo: Reach
- Asset Denial
The playlist is almost entirely dried up so you will need a boosting partner with 4 controllers. Two parties of 4 players (3 guests each) made matching up easier, but you could use more people if you don't have 4 controllers.
This only took us a few tries, but there was one random player searching so we adjusted our server regions found in
" Options & Career > Settings > Network" to narrow the matchmaking field even more. That may not be needed for you. Server regions cannot be adjusted while actively searching for a game. Change from the lobby, then search, if needed.
Hope that helps!