In my opinion, E is the correct choice.
This one isn't too bad, considering it's 2/5 chance. If you are lucky, it will block all the heavy hitters as part of that 2/5 chance.
Dusk, on the other hand, is 6 quanta for a 1/2 chance. 4 quanta for an extra 10%? That is vastly underpowered, especially with the large chance of RNG screwing you over.
The closest shield in nature is Procrastination, which reduces damage by 50% and blocks the use of abilities, and it is guaranteed provided that the creature has at least one attack. Funnily enough, that shield costs 6
.
My suggestion; leave fog shield, or if absolutely necessary, up the cost by one. Dusk should be reduced by two on both, and Procrastination is fine as is.