Want to hear a joke? Silence.

@saby  
Oh, silence is a thing. Forgot that xD

@saby  
Hmm, if randomly targeted minions (like some ogres or Mogor/Noggerfogger on board) can bypass regular taunts, then I think randomly targeted spells might bypass Discord too.

@Liggliluff  
Loatheb? It’s out of Standard play anyway.
 
This one can be dealt with Silence, either via spells or minions, or any sort of minion destroyer effect. Having 4/12 makes it vulnerable to health/attack swap + a variety of common spells.
 
I’ll assume that randomly targeting spells aren’t affected. Or if they are, it needs to be made clear. As in “every enemy spell targets this minion only”.
 
I really like the concept, it’s a very interesting card and suitable for both a HS legendary and Discord as a character.

@Vengir  
There is the card that gives +5 mana on all spells; basically blocking all spells from being used. But that’s just for one turn.
 
This card does something similar (rendering some spells useless); but constantly. This concept might be too powerful.

@Liggliluff  
That would still let the enemy use AoE for positive effects like Circle of Life or Holy Nova. The intention of this card seems to be also preventing the enemy from using buffs.

@Vengir  
I’ve been thinking; the “make the other friendly characters immune” would make them all immune wth two of them.

@Liggliluff  
Oh, I see now.
 
First of all, “Spell Taunt” keyword is not needed… or is the only thing you need as the card text. Keywords are used for commonly appearing mechanics and generally are shared with a bunch of other cards. The only exceptions I know are “Mega Windfury” (Windfury times two) and “Charrrrrge” (works identical to normal Charge). All keywords are explained in additional mouseover windows instead of the card itself.
 
Maybe something like (without keyword) “All enemy spells must target this minion and makes all other characters immune to enemy’s Area of Effect spells”.

@Vengir  
Thinking of it, the wording could be fine for the first paragraph. The second one about Area of Effect I’m doubtful on.
 
Currently; all AoE’s, regardless of owner and regardless of who’s minion it intended to target, it will only affect this minion. – I don’t think that was the intention – and if the target was the opponent’s minions, those won’t be affected, but will this card be affected instead?

@Liggliluff  
Each of your proposed wording would change the way this card was meant to work.

It could be… “Your other character can’t be targeted by spells or Hero Powers”, where the drawback is also that you can’t use your spells or Hero Power on your other minions.
 
Otherwise it could be “Your other character take no damage from enemy spells.”; still targetable, but won’t have any effect.
 
This should improve the wording on your card.

@Famekki  
Apparently. If it works like Taunt, then targeting anything other than this enemy minion gets you “I must target the Taunt minion!” or whatever the exact wording is. So you don’t accidentally Inner Fire this…

Enemy buffs and healing spells also hit him?

Interesting concept to say the least.