Effective masquerade requires an animal to be classified as the wrong object rather than merely to be hard to see. That is a higher bar than colour matching, because a predator scanning leaf litter is looking for anything shaped unlike a leaf.
The dead leaf mantis meets it with structure. An expanded pronotal shield gives the body a leaf's outline, the forewings carry raised lines that read as venation, and the margins are notched and asymmetric in the way a real fallen leaf is chewed and torn. Colouring is mottled rather than uniform, breaking up the surface as decay does. Many individuals rock gently on their legs, matching the motion of litter in moving air, so stillness does not give them away either.
If the masquerade fails, a second layer takes over. The mantis rears back, spreads its wings and raises the raptorial forelegs to present a sudden increase in apparent size, a deimatic display intended to startle a predator long enough for escape.