Riot if you want to rework Molten Shield to be useful... make it a shield.
(E) Molten Shield 20 mana, 10 second CD
Annie and Tibbers gain a shield for 65/90/115/140/165 (+.3 AP), lasting 3 seconds. Enemies who deplete the shield take damage equal to how much they depleted the shield.
Instead of giving up and saying "fuck it, lets go all in on mobility creep", why not just make Molten Shield do its job?
so fuck it.