Cast Hyalopterous Lemure by paying {4}{B}.
When Hyalopterous Lemure enters the battlefield, Jaws of Defeat triggers.
Holding priority, activate Hyalopterous Lemure by paying {0}, giving it -1/-0 until end of turn.
Repeat step 3 an arbitrarily large number of times.
Resolve the Jaws of Defeat trigger, causing target opponent to lose life equal to the difference between Hyalopterous Lemure's power and toughness.

Target opponent loses the game

Infinite lifeloss for target opponent

Hyalopterous Lemure

Jaws of Defeat

Activate Hyalopterous Lemure's ability.
Crackdown Construct gets +1/+1 until end of turn.
Repeat.

Combos with "Hyalopterous Lemure"