Which Xbox 360 downloadable expansion added the best challenge mode?

[killamch89]

Xbox Live Arcade and Marketplace offered great DLC for existing titles. Which add‑on stood out thanks to a killer challenge mode - new tracks, survival arenas, time‑attack courses?

[Scorpion]

The "Halo 3: ODST" downloadable expansion added an excellent challenge mode with its firefight missions. The intense waves of enemies and strategic gameplay pushed players to their limits, providing a thrilling and rewarding experience for fans seeking extra challenge on the Xbox 360.

[killamch89]

Left 4 Dead 2's 'The Passing' DLC added survival mode maps that were absolutely brutal - defending those holdout points with friends became an addiction.