Mogg Flunkies can't attack or block alone.
3/16/2018 If you control more than one Mogg Flunkies, they can attack or block together, even if no other creatures attack or block.
3/16/2018 Although Mogg Flunkies can’t attack alone, other attacking creatures don’t have to attack the same player or planeswalker. For example, Mogg Flunkies could attack an opponent and another creature could attack a planeswalker that opponent controls. Similarly, other blocking creatures don’t have to block the same creature that Mogg Flunkies blocks.
3/16/2018 Once Mogg Flunkies has attacked or blocked, it will remain in combat even if you no longer control another attacking or blocking creature.
3/16/2018 If an effect says that Mogg Flunkies attacks or blocks if able and you control another creature able to attack or block, you must attack or block with Mogg Flunkies and that creature.
3/16/2018 In a Two-Headed Giant game, Mogg Flunkies can attack or block with a creature controlled by your teammate, even if no other creatures you control are attacking or blocking.