The card shows "Ally Mind" within the head and body of this monster.
The name of this card has a dual meaning. A 'Field Marshal' (with one l) is a military rank, which the monster pictured on the card presumably holds. A 'Field Marshall' (with two l's) was a British farm tractor used in the early Twentieth Century. The monster is thus given the name because it is a Machine, like a Field Marshall, and holds the rank of Field Marshal.
According to the Duel Terminal Master Guide, "Ally of Justice Field Marshal" could inspire many warriors the battle field. It was created using "Genex Spare" as its controler, since the Ally of Justice lacked the technology needed to control it. After defeating many "Worms", "Field Marshal" sacrificed himself, and couldn't be repaired.