Prometheus44

The thing with Eidolon is, your deck does 3 damage for pretty much every spell in the deck; it's the entire point of the deck, so doing 2 to yourself in order to do 3 to them is fine if it means they're gonna hurt themselves if they try and play magic/run scared of playing spells. Furthermore, you're locking them out of playing cheap spells because you can "get them dead" any time they go to low on life. Lastly, If you play this guy, and are ahead on board, you're not the one committed to playing a spell first; you can lay beats. This has been one of the best printings for modern burn in a while. Watching some modern burn after this guy was printed might give you a better understanding of why its played in the deck and what its objectives are.

I like the flavour of the deck! That story was pretty awesome =) Anyway, suggestions!
- If you can afford it, you'd really like to be running 2-3 celestial colonnade; It may enter tapped, but it is just too good a card not to play. - Also, mana leak is far better than unsubstantiate in modern. Having your opponent have to play around mana leak gives you the time you need to get your synergies off the ground; it should be a 4 of.
- I also agree with Maniacal that masoleum wanderer just doesnt seem as impactful in this deck either; rattlechains may be better, as it gives all your spirits flash if it's on the field, and has flash itself, or just using those slots to up your paths to 4 and adding a pair of vapor snags may be a better use of those 4 slots, but it comes down to playtesting and seeing if it does enough.
- Finally, starfield of nyx just doesn't do enough IMO; it's a 5 mana commitment and it's only useful to you if you have a fair number of enchantments in the grave already, since the enchantments turning into creatures is not really relevant. Siguarda's aid is kinda in the same boat, since the only thing that really cares about gaining flash is hyena umbra, so I dunno if it's a good call to commit those two slots to something like that. They might be better played as something like spell snare or spell pierce (since modern is a format of a LOT of 2 mana spells). Keeping the aid in for the flavour is totally understandable, but it will impact your decks ability to be versatile.

These are the main things that are sticking out to me.
Good luck with your brewing! =)

Bedlam Reveler is better in a more aggressive build for sure. I think he's the right call if you wanna transition away from delver and build around pyro, cause you wanna cast as many spells as possible as quickly as possible, and he becomes a treasure cruise on a 3/4 prowess body. Maybe build a UR prowess burn deck? Could be neat, with all the super cheap pump and burn spells in the format.

Just a note, if you choose to run thing in the ice, it does not synergize at all with young pyro or delver, so its more of a "one or the other" situation. Price of progress is actually awesome; I'm gonna be trying that myself vs tron (I hate that matchup haha)

Edit: Was too good to be true =( Price of progress is not legal in modern

I've been playing delver for about a year in modern now. My initial build had Spellheart in it, but it's just way to susceptible to removal (read: bolt) to justify the turn 3 play. My suggestion would be to drop the chimeras and the charms, and run +1 mana leak, +1 git probe, +2 spell snare, and +2 spell pierce in their place. The cantrips just function better, and you have a more versatile permission package with that build. I also don't think scepter is mana efficient enough to be run in a deck that really cares when and how it taps, and its hard for this deck to deal with anything bigger than 3 toughness most of the time, so you might consider vapor snag in it's place. Going to board, UR has a lot of difficulty against faster decks and decks like tron and affinity, so for sure consider something like the cards below

2 grim lavamancer (aggro decks)
2 molten rain (tron)
2 vandalblast (for affinity)
2 relic of progenitus (grave hate for dredge and such)
1 hurkyls recall (affinity again)
2 spreading seas (any greedy mana base pretty much)
2 dual shot or forked lightning or izzet staticaster (elves and aggro)
2 roast or lightning axe
2 izzet charm (against slower or control decks)

Your sideboard will depend largely on the meta at your local store or where you like to play. If the meta is 90% aggro and there are no affinity decks, then that will largely influence the kind of things you want in your board. If it's all control and tron, then you probably don't need all the aggro hate. The way you built your deck, with lots of basics also caters very well to blood moon (but I gather you don't want to buy expensive cards), so that might be something you can consider in the future =)

Good luck with getting your deck where you want it to be!

I think if you want something that helps deal against faster decks while still retaining the land destruction, you could go -2 structural distortion, -2 shreds of insanity, -1 demolish and add another worldbreaker for more inevitability and 4 galvanic bombardments. It cuts your dead cards against mono colour and faster dual colour decks, and you can board in something like flames, rending volley, other creature hate for the crumble to dust game 2. Good luck finding the balance!