Flavor text: The biggest problem with our new hires is that they don't want to take instructions.
Another target for discardlock, inspired by Silverware Golem. It's understated for the mana cost as you're obviously looking to discard it in order to summon it for free. Having an immune road block for a turn can be useful for buying time. You can also play it for mana if absolutely necessary to hopefully force interaction with your opponent's board (I hope he doesn't have a ping though!).
This one's actually a bit of joke. When was reading up on the character, apparently it wasn't uncommon for players to try and kill him, up until Blizzard patched it so A'dal made himself invulnerable at low health. I thought that would make for an interesting hearthstone mechanic, so here we go.
So here's how this is useful: either you use it to avoid that minion you played taking damage during your turn, e.g. from Snipe, Baron Geddon, or Wild Pyromancer, or more specifically use it to protect Charge minions like Chillblade Champion. Due to the very situational usage of the card, I think it's justifiable at 0 mana, since it's a very situational spell and it makes Ivory Knight a bit worse by lowering the average spell cost in Paladin further.