Firstly, a special shout out to Effigy for his original "Stealth Bomber guide (Insane/RL bikini winner)" which helped me achieve the dream & win. Also, shout out to Drazhya's "Physical Bomber Tank" for providing the inspiration leading to the winner Stealth Bomber Blasta. The Stealth Bomber is not my original idea, rather I will carry the torch into the next manifestation of this super fun build.
This is my first post ever on the forums, and it happens to be a Spoiler: Adventurer build. So, here we go!
TL;DR Build
Race: Cornac, but really any race works. Just don't pick a smelly Elf and we're cool.
Stats: Mag > Cun > Wil > Favorite Dump Stat, mine was Dex
Class Talents
Cunning/Stealth: 5/5/5/5
Cursed/Force Of Will (unlock 36): 5/5/5/5
Spell/Explosive Admixtures: 5/5/5/0
Psionic/Absorption: 1/0/0/0
(unlock @10) Spell/Stone: 5/1/1/5
(unlock Wyrm Bile) Corruption/Blight: 5/0/0/0
Generic Talents
Celestial/Light: 5/2/5/5 (with Pick your Escorts, otherwise base 1/1/1/3-5)
Spell/Stone Alchemy: 5/0/0/0
Chronomancy/Energy: 5/2/4/5
Spell/Conveyance: 5/1/0/0
Technique/Combat Training: 2/1/1/0/0/0
(unlock @20) Celestial/Hymns: 5/1/5/5
*Scroll down to Strategy for the general leveling guide*
Escorts: Thief = Track, Anorithil = Extra Generic Points, Warrior = Vitality, rest is whatever.
Infusions: Personal Taste, I took Healing/Regen/Mental+Physical Wild/Heroism/Movement
If you don't take a Cornac, then you get 4 Inscriptions not 5.
Prodigies: Lucky Day or Meteoric Crash + Cauterize or Eye of the Tiger (EotT if aiming for base spell crit chance = 100%)
Recommended Difficulty: Insane, because lower difficulties take longer to get rolling, gear and level-wise. It can be done, but it's a slog. I have not tried this out on Madness yet, so stay tuned.
Now, let's dive a little deeper into the build.
Races: Really, any of the races will work for this Adventurer build, even Elves if you're one of those...kinds of people. The guide is based on a Cornac, so taking any other race will require you to be your own boss with your generic points. My advice: if not Cornac, drop Corruption/Blight & figure out your generic point spread on your own.
Class/Generic Point Spread: Again, as a Cornac you're gonna get a bit more points to spend on your trees. My winner also used "Pick Your Escorts" from the ZOmnibus Addon Pack, and iirc I loaded up on Anorithil escorts for "free" generic points in Celestial/"Stop Nerfing" Light. Going 1/1/1/3-5 in Light will be sufficient b/c Providence is the real MVP, and with the metric ass-ton of Crit Multi this class achieves, Healing Light & Barrier are still useful with 1 point so long as you crit. In the end, your Stealth Bomber's point spread will probably be less than my winner. But, that's ok because I believe you will be a winner so long as you don't die! My first Stealth Bomber was an Effigy-design, and that was a no addon vanilla winner. Also, all you need is the vanilla game, no expansions, no Tinkers, just a desire for the power.
Class Talents
Cunning/Stealth: 1/1/1/1 early, invest as needed and 5/5/1-5/5 by end
-what you want to get rolling ASAP is Shadowstrike at lvl 4, that's your gateway to paradise as you grow from a pupa into a deadly butterfly. If you think you'll be short on Class Talent points, a good place to cut down is Soothing Darkness. That's more of a convenience, but I noticed it paired well with Lucky Day prodigy. 1 point in Shadowstrike goes a loooooooong way, as does Shadowdance at lvl 12. Oh yeah, be a good ogre and get Shadowdance at lvl 12.
Cursed/Force Of Will (unlock Lvl 36): 0/0/0/0 early, 5/5/5/5 end
-Shout out to Drazhya for including this tree in the build. In order for Adventurers to have success they need to have ways to continually get stronger through talents, and not by relying on gear to do so. This tree fulfills that need. Don't worry about it early, you have more important skills to attend to. Once you are ready young butterfly ogre, which is around the time Stone's tree is finished, start pumping points into this tree & DO NOT trim any points from this tree. This tree provides a massive crit multiplier while giving you a couple more options on offense. Yes! Fist Pump!
Spell/Explosive Admixtures: 5/5/5/0 early-to-mid
-The early game Stealth Bomber is tough, there's no mistaking it. The Stealth Bomber's greatest power is also it's weakness; Throw Bomb is atrocious early game, and even with Shadowstrike it makes for a difficult T1 dungeon experience. I'll discuss strategy later. For now, the point investment is your call. Experiment with what works for you. Go easy on Explosion Expert until you feel comfortable with Alchemist Protection. Me? I'm comfortable at 100% Protection b/c I'll blow myself up without it. Don't wait on going 5/5/5/0 though, try to finish it around lvl 16-20. Also, feel free to experiment with Shockwave Bomb & post your findings. Having an extra attack skill would help.
Psionic/Absorption: 1/0/0/0 at start & that's it! Wow!
-The quintessential Adventurer Tree, 1 cat point + 1 class point =

Spell/Stone (unlock lvl 10): 5/0/0/0 asap, 5/1/1/5 mid-to-late
-This is your other attack, and it crits from Shadowstrike. Get 5 points into Earthen Missiles as soon as you can. I understand it's difficult since Admixtures needs attention & a point needs to go to Shadowdance at lvl 12. You're so close to tasting the power, just keep pushing! Once you have your bases (ie Admixtures & Earthen Missiles) finished, proceed to pumping up Crystalline Focus, with a dash here & there into Stealth as needed.
Corruption/Blight (unlock Wyrm Bile): 5/0/0/0 very last points
-Overkill crit multiplier. That's about it. It's here where the build can use some input b/c I can't help but think there's a tree out there that can improve the all-around attack power of the build. Maybe something that adds more activated spells? Input would be greatly appreciated here.
Generic Talents
Celestial/Light: 1/1/1/1 early, 1/1/1/3-5 as needed
-"Just as Branzir continues to chase Ralkur, Dark God continues to nerf the Light" -Tokugawamasamune.
Providence is why you take this tree. If you find you have a surplus of generic points, imo, you can never go wrong putting them here. Some players bash Barrier, but I like it's 10 turn duration, and with this class's crit multi you're looking at a damage shield valued at around 2000 pts with 5 points invested, unadulterated by Aegis or other shield buffs, which you get with Bathe in Light.
Spell/Stone Alchemy: 1/0/0/0 early, 5/0/0/0 as needed
-Necessary to run any bomb-based builds. No explanation needed really, just put a point in as the equipment tier increases. Regarding what gems to turn into alchemy gems, 99.9% of the time I use +dmg% gems. Feel the power!
Chronomancy/Energy: 5/0/0/0 early, 5/2/4/5 mid-late
-This is the Stealth Bomber's utilities program. It has your damage mitigation, ability to double-strike with bombs & missiles, and Entropy. This tree is just plain awesome, and really compliments the Stealth Bomber by making the build adaptable to all encounters. Energy Decomp is damage mitigation. Energy Absorption has its uses. Redux is usually bashed and seen as a waste, but not here. The Redux-Opener-to-Double Bomb-In Yo Face will help you greatly in the final battle, and all battles for that matter. Entropy is the attack form of Providence. What else is there to say?
Spell/Conveyance: 5/1/0/0 sort of early
-This is your evasion. 1 controlled phase door and 1 panic button. Invest as you see fit, but know that a 5-point phase door early playing on Insane difficulty is great, and since you are delicate & weak in the beginning it's a good place to start putting your generics. I do, and I am a Stealth Bomber winner 2 times over

Technique/Combat Training: 2/1/1/0/0/0
-No points in Accuracy/Weapons/Daggers. When you have the 16 strength needed provided by stat boosting gear, put a point into heavy armor training. 1 point into light armor is fine if you like. I like, therefore, I do. I had 2 spare generics so I dumped them into Thick Skin. No heavy/massive armors, leave that to the heavy bombers. We're going stealth mode here, can't do that with the heavy armaments. But fyi, heavy gloves & boots are fine for stealth.
Celestial/Hymns (unlock at lvl 20): 5/1/5/5 mid-late game
-And here is my contribution to the build! The Hymns tree will provide a good boost to your crit multiplier, plus infravision if you need to boost your radius. Hymn Nocturnalist is nice for the 20% blind chance + extra darkness damage, which crits! I was fortunate to roll up a merchant randart lantern which gave +0 light radius & +8 infravision radius, so having that extra +3 infravision from Hymn Adept matched perfectly with the build. Best believe that lantern will get vaulted to every stealth bomber from here on!
Gear
Stacking your gear stats is so easy with this build, even an elf can do it! We're looking to stack on: Crit Multiplier, Physical Damage, Physical Penetration (aka the Big 3). That's it. Yeah! Really! That's all you need to be successful with this build. Keep pumping Crit Multi, pump Physical Damage, get Physical Penetration to 100%. Simple as an elf! Maybe have 1-2 pieces of "Mana on crit" gear, and something that grants Track too if you didn't get it from the Thief escort. But yeah, prioritize those 3 areas of offense over extra fiddles like +stats/life, heal friendly summon, etc. Now, it should go without saying but just in case, make sure to "Command Staff" to physical affinity. And try not to neglect your resistances too much. Oh, and get a wand of clairvoyance asap, with a big radius.
Keep an eye out for 1 handed "short" staves because you can wield a dagger/mindstar in the off-hand slot. You don't have to pick an Ogre to take advantage of the TK-wield/Main/Off-Hand trifecta of weapons. I have a TK wielded Blighted Maul artifact b/c it's better than any staff for this build, plus a mean 1-hand randart staff, plus a mean randart mindstar. I mean, just look at all that sweet crit multiplier & physical fiddles and stuff! Don't try to overthink the gear on this build, go with what grants you the most of the Big 3. Also, make use of the training dummy to determine what combination of gear grants the most damage if you find yourself hoarding items. Fyi, if you didn't know, the Sher Tul fortress is a great place to store items, just drop them on the floor. I like to hoard artifacts myself, kinda like a personal collection.
Also, and pay attention because this will get you killed if you ignore it, find a backup staff with mana regen activate ability (manaflowing staves I think) or a mana surge rune ASAP. Otherwise you will have no way to restore your mana when it gets completely drained by a mana clash or some other form of resource burn. IT WILL HAPPEN, and you won't be able to rely on "Mana on crit" gear to get back into the fight. Better have a movement infusion too b/c no mana means no tele-panic button. It'll take 2 turns to swap weapons + activate, more than enough turns to insta-gib your ogre butterfly ass and get clobbered into soup.
Strategy
General Leveling Guide
First, take out any points you may have in any talent listed as "is a spell." Ogric Wrath is a prime example. Now you'll be able to access Zigur, which sells torques of mind blast. YOU ARE GOING TO WANT ONE OF THESE TORQUES. They will make your time in the early game so much easier. You can do without, but it's going to be tough. Don't start unlocking trees and assigning points. Just go straight to Zigur.
Start: Class Trees = Cunning/Stealth, Spell/Explosive Admixtures, Psionic/Absorption
Generic Trees = Technique/Combat Training, Spell/Conveyance, Spell/Stone Alchemy, Celestial/Light, Chronomancy/Energy
*If Cornac, you can add an Inscriptions at the start. Also, make use of the "Hide unlearnt categories tab for quality of life.*
Up To Level 10: 1 point into stealth & shadowstrike will do, focus on improving admixtures. Explosion Expert will improve attack power, just don't blow yourself up. Get your Conveyance to 5/1 and then start working on Energy Decomposition, pump it to 5. Don't worry about Light at this point b/c your magic isn't strong enough.
Up To Level 20: Unlock Spell/Stone at Lvl 10. Get Shadowdance at Lvl 12. From here, fill out Explosive Admixtures while getting Earthen Missiles to 5. It's here where you begin to feel the power! After getting Energy Decomp to 5, proceed straight to Light's Providence and pump to 3. Then back to Energy and get Entropy to 2 or 3.
Up to Level 30: At this point you should have a good feel for how the build works. From here, the build continues to add +Crit Multi through talents, while rounding out the Cunning/Stealth tree. First order of business, unlock Celestial/Hymns with your Lvl 20 cat point. Now, focus on finishing the Spell/Stone tree at 5/1/1/5. From here, fill out the Cunning/Stealth tree as you see fit. You may find yourself carrying a couple of Class Points and that's ok, you'll use them quick after unlocking Force of Will. For your generics, it's here you want to get Redux to 4, now you can double up Throw Bomb & Earthen Missiles. Nice! Finish rounding out the Light & Energy trees before investing into Hymns. Hymns are for improving damage, whereas Light & Energy keep you alive. I want you to stay alive!
Up to Level 40: Prodigy #1 is your choice. I took Cauterize first b/c I got overconfident and died 3 times. Cauterize is great for mitigating user failure

Up to Level 50: Just a matter of filling in the blanks now. Prodigy #2 is your choice too. I like Lucky Day & it synergizes well with your stealth, and the 10% chance to avoid damage is a bit o' terrific. If you focused on 100% base crit Eye of the Tiger would be nice too. Each point put into Force of Will makes you do more damage. Hymn of Detection makes you do more damage. Dark Ritual makes you do more damage. Not even JC Denton can see the death your bombs bring from the shadows. Can anything stop you at this point?!
How To Play
I'll keep this part short b/c I don't want to tell you how you should play, and any sort of deviation will be wrong and call you an elf because you failed.
So here's the thing, you are not a warrior. Energy Decomp is not your ticket to tankdom. Use the grand radius of your bombs to gib the unseen around corners. Break Line-Of-Sight when Stealth is off cooldown to quickly activate it. Shadowdance lets you stay in the battle for an extra attack. Wands of clairvoyance synergize fantastically with the Stealth Bomber. Redux--Throw Bomb x2--Shadowdance--Earthen Missiles--Phase door away is a powerful combo, but you will have to time your Stealth cooldown to use it (ie when Stealth is 1 or 2 turns away use redux). You don't have a lot of attacks to use, so Gwai's burninator & Rod of Spyridic Poison are valuable.
And lastly, have fun! Feel the power! And die a couple times from overconfidence!