I'm not sure about this card. Isn't this just a mixture of Aflatoxin (with more poison damage) and Balisk's Blood (with a shorter stun duration and no HP increase)? Its deadliness can be pretty effective against certain enemies (dragons, for example), but the fact that it's a single target spell makes me feel that it can be situational at times if you're facing enemies with extreme HP (Gravity), abilities to negate it (Light), or cards to undo or become immune to the effect overall (Time and Aether).
For some reason, I feel like if the target dies from a Deadly Neurotoxin, it should... you know, spread like a deadly neurotoxin, to a random adjacent target. That way, it's like plague, but only affects one target at a time (assuming they're close).