If this card is in your hand and all monsters you control are face-up Reptile monsters (min. 1): You can target 1 face-up monster your opponent controls; change its ATK to 0, and if you do, Special Summon this card, then take damage equal to that monster's original ATK. If this card is sent to the GY as Synchro Material: You can target up to 2 face-up monsters on the field; change their ATK to 0. You can only use 1 "Reptilianne Lamia" effect per turn, and only once that turn.
After making an enemy monster’s attack 0, use Reptilianne Lamia to make Reptilianne Hydra. Reptilianne Hydra will destroy all monsters with 0 attack on your opponent’s field and let you draw a card for each monster destroyed.
Your mention of handtraps is irrelevant. Lamia is not a hand trap. The reason hand traps are good is because they disrupt the opponent's plays. Lamia's effect is not a Quick Effect, it doesn't interact with your opponent's plays whatsoever.
Monsters with ignition effects are not hand traps. (Granted, it's a fan-term, but the whole point of hand traps being special is responding to the opponent's plays. A card like Lamia, Electric Virus or Thunder Dragon doesn't do that.)
Why would you run Life Cost 0? Lamia makes you take effect damage, not pay a cost. You're better off running Light & Dark from Lumis/Umbra with 1 copy of Alien Grey, that can be searched off "A" Cell Recombination.