Roll Player: Monsters & Minions
Buy this firstBGG rates it 8.0 from 4,910 ratings. Owners call base + M&M 'the full game' and it is the only expansion with a 5th-player set and boost dice.
Needs: Just the base game
Adds: A final monster with rumors that reveal its lair, obstacles and attack, plus minions to hunt. Adds boost dice, five character sheets, 170 cards and a 5th-player set.