Designer: https://boardgamegeek.com/user/Eps01

Status: [ In Development | α | β - Beta | Available ] | Reference implementation | BGG page

Terraforming Mars: Underworld is a fan-expansion that re-focuses the game on the main Mars board, by introducing a second layer of resources on it, buried deep beneath the surface. It also introduces a new resource: Corruption, which adds depth to corporate warfare, as well as to cards with negative score.

This new expansion focuses on the Mars board and all of the riches hidden beneath its surface. Identify spaces on the board to find valuable underground resources, then Excavate them in your bid for victory. As a side benefit, the network of tunnels you’ll create is an ideal place for various shady activities, outside of UNMI’s prying sight. Use your connections with the criminal world to stave off assaults and act with impunity. But watch out! Get too corrupt too quickly, and you’ll find yourself on the receiving end of a Class-Action Lawsuit.

The basic functionality is available, including

• Identifying and excavating underground resources
• Collecting corruption, using it to block damage, engage in Turmoil collusion, and end-game score bribing
• 86 project cards (of 90)
• 11 corporations (of 12)
• 14 preludes (of 15)
• 5 global events
• 2 awards
• 2 milestones
• No colonies or anything not mentioned.

• U12: Social Engineering - Using another player's action crosses too many issues.
• [Corp] Ares Media. It's doable, but it's another "event cards are face up" corporation, but we don't need another one.
• [Prelude] Intellectual Property Theft - Copying another player's face-up Prelude might clash with Prelude 2. Maybe it can be literally duplicated in an online format, but that also leads to issues not worth chasing down for one card.
• [Colonies] Amalthea, Phobos, Oberon They all seem kinda OP, don't they?

• U82 Class Action Lawsuit
• U83 Mercenary Assault
• U86 Media Frenzy - though the only person so far that seems to think this card makes sense is the designer.
• Replacement Standard Technology