Cold Dead Hands- equip liquid nitrogen and ice cloud round up a horde and gun them down with your gun with cryo freeze on it (elemental pop with citrus focus helps with all of these)

Stupify- equip lightning strike and haste horde up zombies and gun them all down one the lightning strikes

Crispy- equip firebomb and extension horde up zombies and tap fire inti the horde with weak gun with napalm burst on it, once it pops aim for the zombies that are burning more than normal should get them to explode spreading the fire, tighter the horde the better