Also, you can use his effect on "Reptilianne Gorgon". Not only does it allow "Gorgon" to attack an opponent's monster without being destroyed, but it also protects it during your opponent's turn. Also, since this card is easily banished from the Graveyard, it doesn't conflict with "Viper's Rebirth".
You can Special Summon this card by the effect of "Junk Synchron" or "Debris Dragon", Synchro Summon a monster, and remove from play this card to protect that Synchro Monster from battle next turn.
This card can work in a "Gladiator Beast" deck, as it protects them so they can attack and then switch out with another "Gladiator Beast".
Use in a direct attack deck with "Raging Flame Sprite" to protect it until it can power up with its own effect.
Sometimes your opponent has many powerfull monsters, defense position monsters (that can't be destroyed by battle), or tokens that protect him. Summon a monster with low, or even 0 ATK (like "Effect Veiler" or another "Necro Defender"), use "Necro Defender's" effect on him and switch it to your opponent's side of the field with "Creature Swap". You take no damage, but your opponent WILL, so summon high attack monsters and attack "Necro Defender's" target to inflict some serious damage or even make an OTK.