Creatures are a big thing in common only formats, so I don't think I'd recommend the Phantasmal Bear , there will generally be something like a Young Wolf or a Phyrexian Rager to stand in it's way, even worse is that it dies to Death Spark . By cutting creatures you make Fiend and Delver much stronger. For this reason I would also cut the Mogg Fanatic , I just don't know if he does enough work alone to be good in this deck. The option of being able to deal one damage to a creature is incredibly powerful, but I think just having burn spells would be stronger.
In my experience with Kiln Fiend decks, Wee Dragonauts is a bit slow. I've cut him from dedicated Fiend decks before, and this isn't even that. It's up to you, but I'd cut him.
You probably don't want Mana Leak because it's a responsive spell.
Preordain is better at filtering, Brainstorm is better at setting up Delver of Secrets . I guess Ponder is a compromise between the two? When I play a blue Pauper deck I will usually run four Preordain, with Delver in the mix though things become a little hazy. My Delver deck runs four Preordain, three Ponder, and three Brainstorm. I'm not telling you to change anything here, just to consider your options carefully, because it will have a fairly big impact. You might even want to run more than four filter spells, since they are a great way to enable both Delver and Fiend.
I'd definitely run the standard three damage burn spells for . I see you already got a full set of Lightning Bolt . I think I'd add in a fourth Chain Lightning and perhaps even run Rift Bolt and Lava Spike as well.
Jilt might be too slow for this deck. It only runs twenty land after all.