This will include early game, hardmode, optional bosses, and events.
Guide to Boss and Master Mode Progression
Craft a house, explore the world, find crystal hearts underground to upgrade HP, find stars to upgrade mana. Find chests to find gear, mine to craft gear. Early game enemies will be difficult until you get some armour and better weapons.
King slime (optional)
This boss is optional, nothing exceptional about him. He's stronger than previous game modes, has higher HP. You still want to avoid his attacks by moving when he jumps. He will move and squeeze through between objects.
If you were able to defeat the goblin army (random invasion) you will unlock the goblin Tinkerer NPC. He is very crucial for success in master mode as you will be able to modify accessories by adding stats. You will want all six accessories (any) to have warding mod which will give you +4 defense each. Full set of warding accessories and a gold/platinum/molten armour set will negate almost all of the damage in the early game.
Eye of Cthulhu
Can be very deadly if you fight him early in the game. Recommended to have a full set of gold/platinum/bee/molten/etc gear, and a bow with plenty of ammo, or a gun. Focus on dodging, can build an arena with camp fire to help regenerate HP. Spawns after having 200 HP at night or by using the craft item. It is good idea to have full HP of 400 before you fight him. His rampage mode will dash very quickly dealing a lot of damage, so beware and try to have good movement.
Eater of Worlds (Corruption world boss)
You will want to dodge by simply moving aside when it moves, it is recommended to have a weapon that will hit multiple parts at once, and deal a lot of damage. Having high armour will negate all damage, kill the adds to get HP back. Make sure to jug life potion whenever you can if you run low.
Brain of Cthulhu (Crimson world boss)
He will spawn 20 creepers that will overwhelm you, they must be killed first. If you don't take out the creepers the boss won't take any damage. On the second stage it will start to hit you and teleport around while having mirror images.
Found by talking to old man in dungeon, be prepared to dodge a lot. Defeat the boss to gain access to the dungeon. The dungeon will have some useful equipment. If you fail to defeat him wait until next night. Entering dungeon without defeating the boss will kill you.
Queen bee (optional)
This boss is completely optional as well, you don't have to fight it unless you want to craft a bee armour for summoners. Horizontal sweeps, and flying attacks.
Wall of Flesh
The last boss of early game, you will want to build a classic hellbridge from the beginning of the world to the end. To summon throw a doll to lava. Be prepared to enter hardmode as you won't be able to go back. Recommended to have hellforge armour and pickaxe before proceeding.
Before doing anything you will want to spawn the new hardmode ores with pwnhammer from WOF.
How to spawn the hardmode ores.
When i say run, run!
No kidding, everything is deadly, you will die, and a lot. Start by digging around, and keep digging around enemies. You will want a molten pickaxe from early mode to dig the new ores. There's 3 different ore types, you need the pickaxe from previous tier to mine the next tier. After you have a hardmode armour and gear, you will be able to start fighting back the enemies. Also now you can find the jungle and find 20 gold hearts to upgrade HP from 400 to 500.
You will want a set of wings to help you fight this, and you need a hard mode armour set. I recommend getting a ranged weapon for this fight, as you will need to hit and kite. Easiest wings to get is build a house in the jungle and buy leaf wings from the doctor.
Defeating this boss will allow you to create the megashark, the strongest early game gun. (mini shark + illegal gun parts from gun merchant + shark fin + soul of might). Beating both the destroyer and twins will allow you to create hallow armour and gear. You will want to move and round and avoid his hits, as he will hit hard.
Recommended to have a ranged gun, just avoid his hits and move around as needed. Beating all 3 mechanical bosses will allow you to craft a minecart, and access to the next boss: plantera.
Queen Slime (optional new boss)
It will jump around and spawn minions, in second stage it will fly and attack you relentlessly.
After defeating all 3 bosses,head to the underground jungle to find a plantera bulb. This can be very frustrating, in your way down there you can find Chlorophyte Ore which will allow you to create the second strongest tier of armour in the game before the end game. To mine it you will need to craft Drax, the materials are from the mechanical bosses. 18 hallowed bar + soul of fright, might, and sight.e keys. Also you can fight golem next.
Dig around the jungle until you find the temple, you will need a temple key from plantera to access it. After defeating head to the dungeon.
Duke Fishron (Optional)
You will need a fishing rod and truffle worm. Head to the ocean, cast your fishing rod and unleash the beast. While this boss fight is optional, it will give some strong equipment and a infinite flying mount.
Empress of Light (Optional)
Bullet hell, good gear. Special drop if done during day, kill a bug in the hallow area.Very difficult fight, recommend to have golem tier gear.
Go to the entrance of the dungeon, kill the cultists to start the boss fight. Will summon clones, shoot various attacks, and use a dragon pet. Defeat him to start the lunar events.
Four pillars with different enemy types, defeat 150 mobs, then defeat the pillar. Collect souls to craft weapons, and moon lord summon item. Can be found throughout the world, defeating will summon moon lord.
The final boss of the game, very deadly. Can use different strategies, but I recommend doing something similar to my video. You can also try to fly and dodge with a mount if you want. Will kill almost any geared characters with laser. Beat him to end your journey, or begin it. Can craft the best armours in the game with his loot.
Can occur naturally, must have destroyed shadow orb or crimson heart. Need to have 200+ HP.
After defeating one mechanical boss, it will occur naturally. Can also summon with solar tablet.
It happens naturally after defeating wall of flesh and destroying one altar. Can also be summoned with pirate map (which drops from enemies in the ocean). Can use goblin battle standard to summon it.
Can be summoned by using a snow globe. No bosses or anything special, will summon santa NPC after it's defeated.
Old One's Army
Speak to tavern keep NPC to buy the altar and gem. Place the altar in a very open field, and then place the gem to start the event. This will have wave of enemies, and various mini-bosses. It's recommended that you buy sentries from the NPC, to summon a sentry you will use mana from defeating waves. Beating them will give you medals which you can use to buy set of gear after defeating mechanical bosses.
Halloween event, you will need to use pumpkin moon medallion, use it during night time. It will summon waves of enemies, each stronger the previous. 15 waves, drops good loot.
Another christmas event, you will need naughty present at night to summon it. Spawns very difficult enemies, has good loot. 20 waves total.
After defeating golem you can find a flying UFO in outer-space. Listen carefully to find one. Let it get away, teleport home, and the event will start. Drops cool stuff such as flying UFO mount.
Zenith: the strongest sword and weapon in the game, to craft it you will need a lot of items from the beginning of the game to from events, and even moon lord.
Terraprisma: A cool summoner weapon that will summon swords to attack your enemies. Must defeat empress of light during day time, to defeat her avoid getting hit as she will one shot anyone.