Othell skill questions

So about Reverse...what warrants it a 5 min cooldown? It doesn't seem very special to me.

Secondly, Dark Paralysis's description says "causes enemy's body to go completely rigid for 10 seconds and paralyzes for 5 seconds afterward". What exactly does the first part do?

Also if I wanted to enchant my skills with blessed enchanting, do I only need to use a mastery codex once or do I need to use it for each time I want to blessed enchant?

it reduces stats like speed, cast speed, attack speed...
how much? i don't recall.

sounds like the old school hold skill for necro's except with more debuffs