The Welcome to the Abyss Add-on for Trials Fusion has 5 achievements worth 250 gamerscore.
Finish all of the hidden Ancient Warp Zones
Complete the 'Awaken the Kraken' challenge on 'Deluge'
Pass the thunder storm in 'The Long Haul' whilst on fire!
Find all 3 squirrels on Welcome to The Abyss
Pass all tracks on Welcome to The Abyss