K. AFTER THE SECOND FLOOR

After your first Devil room, if you're still underpowered, you're going to find out very quickly in the Caves/Catacombs.As soon as you enter a room, hit escape while you think through your plan. (I never did this, but it's a great idea.) Which enemy needs to be eliminated first? How long am I safe at the door? Am I safe anywhere?Speed, range, damage and spectral tears give you options. Having an "oh ♥♥♥♥" active item or card (invulnerability, teleport, damage surge) is really nice, but you have to practice using it in a pinch.Without Dead Cat or an "oh ♥♥♥♥" item, you'll be hard-pressed to survive to Mom, unless you're incredibly lucky and don't hit any unavoidable-damage rooms. And there are LOTS of them. Bonies, Blubbers, [Gazing] Globins, Hoppers, Leapers, Hosts, Knights, [Red] Maws, Splashers, Ragling, Crazy Long Legs, Wall/Blind Creeps, and Tumors can end your day quickly if in a difficult configuration or if you're not paying attention.And then there are the bosses. Gurdy Jr. is the worst, followed by Mega Fatty. The former is easy if you have something to slow him down or if there's a few obstacles to hide behind. The latter -- just keep moving to avoid his jumps, and watch for his sucking move. In Catacombs, Peep's the worst, because his floating Peepers have much larger hitboxes than you'd like to think.If you've gotten to The Depths/Necropolis, you've proven the viability of The Lost, and these next two floors are more of the same. If you haven't just been lucky, you probably have a decent shot at Mom.Risky Bosses: The Cage, The Adversary, Double Haunt, Double Gurdy[Necropolis only]: The Bloat, Daddy Long Legs, Gate, Triachnid (rare)Mom's Foot is usually pretty easy as the enemies are easily dispatched and the stomp predictable.The Boss Rush is hellish, but if you got here in under 20:00 there's really no reason not to attempt it, if only to see how far you get. If you have extra lives and there's a good item in the Rush pool, even less reason. I got it on my first try. Mom's knife is typically what you'll need to successfully pull it off -- along with high speed, damage and range.Boss Rush or no, after defeating Mom you need to decide whether to take the Polaroid or the Negative. If you feel seriously overpowered against single targets, take a shot at The Lamb; otherwise you should play more conservatively by going to The Chest (where you get four free items, and Isaac/??? are generally easier).The Womb/Utero is where high single-target damage becomes important. Fortunately for The Lost, fewer enemies means more avoidance options and faster/safer room clears. Floor 7 bosses are straightforward, too, although It Lives! can be quite challenging if you've been relying solely on offense and dodging. There's a lot of lasers and tears to dodge, and god forbid a Teratoma should be summoned...Remember that Floor 8's Devil room is always empty, and you don't get an item from killing It Lives!, so if you have the Negative you have the option of skipping the boss without any cost and going straight to Sheol.This floor is comparable to The Womb, and the boss is arguably easier than It Lives! Isaac (boss) has three phases:Phase 1. Just keep moving around Isaac and attacking until he gets up.Phase 2. Angels are added but generally stay to the side of the room, taking out the angels quickly and firing consistently on Isaac.Phase 3. If you're fast, use the corner below the origin point of the light beams to 100% dodge them. The upper corner opposite it is also [almost?] always safe.Again, the floor itself is pretty easy. However, Sheol's boss is significantly harder than the Cathedral's.If you're fast, save active item damage for Phase 2 (Satan's first form). If you're slow, you'll probably need it on Phase 1 (The Fallen). Phase 3 (Satan's second form) is the easiest: just keep killing Leeches and keep moving around the room, predicting the food stomps and avoiding them.If you managed to save an Emperor card, this is the time to use it. If not, careful of [Dark Room] Camillo Jr, Null and Wizoob.The Lamb is scary. Once the boss separates into two parts, keep moving -- The Lamb can insta-teleport right on top of you, killing you instantly. Take out the body and then finish off the head.??? isn't very scary and after all the items you get in the Chest, you'll probably dispatch him faster than you did Isaac.