If you're referring to the Elder's Sigil, then yes. However, that is required for a different activity. "Challenge of the Elders" is a level 42 gamemode with 3 random bosses and no enemy waves. "Machine Wrath" is a level 32-34 (depending on rotation) gamemode with regular rounds of POE that have a specific layout and it always ends with the boss "Kaliks Reborn." I apologize if my words confused the two.