you can sacrifice the weapon you have in you're hand
Only drops the bladed ring after sacrificing the the weapon 
Plugirism
Sources and community notes
- The 0.1.10 patch notes say the Pugilism Altar now spawns more often.
- The Secret Rooms guide has now been read in full and does not mention the Pugilism Altar, so the only sourced detail remains the 0.1.10 spawn-frequency change.
Community-sourced (added October 2026, not yet verified in-game). Sources: Steam patch notes 0.1.10 (Aug 5, 2024); Steam guide: Secret Rooms and You by Slunky.