http://brickset.com/sets/7649-1/MT-201-Ultra-Drill-Walker
"This powerful drilling rig may look like a simple base for mining energy crystals, but it's so much more -- when hostile aliens attack, the MT-201 Ultra Drill Walker converts into a massive 4-legged mobile tank-mech and thunders across the surface of Mars! Includes 2 astronaut minifigures and alien commander! Detach the high-tech observation shuttle to keep an eye out for the Alien Commander and his strike ship! Launch the missile at the alien attack ship! Turn the gear to spin the drill for mining energy crystals!"
Missing and replaced Parts (last updated 2017-03-07):
-Missing Part 30396.
-Missing Part 57587.
-Missing Part 62694.
-Missing Part 62724.
-Missing Part 2335pb112.
-Missing Part 3068bpb1038.
-Missing Part 45705pb019.
-Missing Part 62723pb01.
-All other stickered parts not mentioned on Bricklink.
-Part 2446 replaced with Part 30124.
-Part 2456 replaced with Part 44237.
-Part 30360 replaced with Part 93168.
-Part 32020 replaced with Part 86652.
-Part 32064b replaced with Part 32064.
-Part 4265c replaced with Part 32123.
-Part 57910u replaced with Part 92013.
-Part 60176 replaced with Part 93571.
-Part 6019 replaced with Part 61252.
-Part 60470 replaced with Part 60470b.
-Part 6538c replaced with Part 59443.