All creatures your opponent control lose flying.
Magus of the Moat prevents things without flying from attacking.
Creatures your opponent can not fulfill the conditions necessary to attack.

Opponents creatures can't attack

Archetype of Imagination

Magus of the Moat

All creatures lose flying and Islandwalk.
Magus of the Moat prevents things without flying from attacking.
Creatures can not fulfill the conditions nessasary to attack.

Lock in which no creatures can attack

Mystic Decree

Gravity Sphere causes all creatures to lose flying.
Magus of the Moat prevents non-flying creatures from attacking, and since no creatures can have flying, no creatures can attack.

Combos with "Magus of the Moat"