I've started an ironman coop around two months ago, and I've gotten pretty far(300 hours, coopmates have 1500+ hours total). I see alot of people asking for help on starting an ironman, as well as people going about dungeons in a terribly inefficient way. Hopefully this guide helps you progress on ironman in the best way. (I won't be covering parts of the profile such as fishing, foraging, slayers, as they are super straightforward)
Earlygame Before going into the deep caverns, you should do a couple things. The first thing you should do is farm wheat for money. That should make you enough money to buy growth 1 diamond armor from the armorsmith npc. You can buy multiple sets, and combine them for growth 2/3/4/5 diamond armor. You should also buy an undead sword, and enchant it with smite(buy and combine books from the librarian)
The first thing you should do when you get to the deep caverns is unlock all the layers quickly(click to learn how) Go straight to the diamond reserve, and head left, to the tunnel between the diamond reserve and obsidian sanctuary. This area should be free of mobs, allowing you to farm diamonds. Get a diamond pickaxe, enchant it, and go to the lapis mines. Here you should grind full lapis armor, and enchant it with growth 5 and protection 5(enchant table crafting materials can be bought from builder+librarian).
The next part is to farm 130k coins from killing the obsidian sanctuary mobs(scavenger talisman + scavenger 3 is very useful). Enchant your undead sword using the exp you get. Once you have 130k, go to the park, and wait by the melancholic viking. You won't be able to complete the quest yourself, however, if you wait a few minutes, someone in your lobby will probably come and do the quest, allowing you to access the shop as well. You should buy yourself raider axe. This weapon will be your main weapon until you are pretty deep into dungeons.
Midgame Contrary to popular belief, the end is actually really useless for ironman profiles. Don't bother with the end until you are grinding obsidian for the treecapitator. It isn't worth it to get an aote this early on, just stick to a grapple hook. The only thing you should do here is mine some endstone for an end biome stick, so you can farm endermen on your island(unless you can one tap 4.5k endermen). This will give you pearls that you can use to travel around and get fairy souls. After you have some shadow assassin armor, come back to get an aote.
Doing dungeons as a lapis non? Yes, I genuinely think this is the best thing to do(if you are trying to progress as fast as possible) Entrance mobs only have 15k hp, which is really low. You should start as tank, so you can use your ultimate to gain 5 seconds of invincibility, and seismic wave to do 10k damage, and finish the mobs off with your raiders axe. The automatic respawn timer is very short as well, so even if you die it doesn't really matter. Try to get a full set of random pieces of dungeon armor, which can then be used to get a full set of heavy armor.
At this point, most people would grind through floor 1, then floor 2, then floor 3, and so forth. But, this is a complete waste of time. There is no need to grind any of these floors at this stage of the game. Alternatively, you should just join collection or speedrun parties on party finder. These parties will usually have at least one person that can clear the dungeon + bossfight by themself. Just stay behind and do secrets while your teammates deal with the dungeon. Your goal here is to get healing potions, as well as completing floor 1, 2, and 3 at least once.
Tip: Play as healer, and heal yourself in a wire trap. This will allow you to reach milestone 3 without actually fighting any mobs
Doing so should unlock floor 4 for you. This floor is special because of the thorn bossfight. In the thorn bossfight, you can use the decoy strategy. This means you can go through the entire bossfight without taking any damage. You will also be able to hit the bats to reach milestone 3, which means you will get cata xp even though you didn't fight anything. This floor will allow you to grind up to cata 16, allowing you to join decent floor 5 parties, as well as unlocking the hyper cleaver(your next weapon).
Before you begin floor 5, you'll need alot of money. Hyper cleaver costs 800k, and shadow assassin armor costs millions of coins. After the farming nerf, I firmly believe that sugar cane is the way to go. Build yourself a 3 layer sugarcane farm, and farm lots of coins.
Lategame
Once you start doing floor 5, your gear won't be good enough to survive. You should still stay back, and focus on secrets. (You can play as healer to get milestone 3) Doing so will hopefully, with decent teammates, allow you to do S runs. Your goal here is to get 3/4 shadow assassin armor from the obsidian chest(or a livid dagger if you're lucky) This will also get your catacombs level up, which will allow you to join floor 6 parties.
Tip: Start your own parties in party finder, you'll still get good people as long as your catacombs level is not extremely low
The only purpose of floor 6 is to get a flower of truth. What you should do in floor 6 is do collection/speedrun parties. In the bossfight, do golems before terracottas. When they are close to dying, jump in front of the golem to try to pick up the ancient rose(if it drops).
Rose drop rate: 10% per golem
I haven't reached floor 7 yet, so I can't give any advice for it yet.
Assuming you followed the dungeons spoilers, you should have pretty good stuff. This is a good opportunity to go back to the end, and grind a treecapitator, as well as an aspect of the end. You should be able to handle tier 4 slayer bosses as well. You can basically go any direction you want from here on out.
That's all for my guide! I know it skips many areas of skyblock, but if you want to progress as fast as possible, this is your best shot.
