Infinite money and XP:
Use the following trick to easily farm money and XP early in the game, right after you have defeated the first main boss. It is also risk free since there is no chance you will accidentally die and lose a lot of your saved money. Simply go to the "Gun Fort" sculpture idol in the Sunken Valley area. Then, go back to find an enemy with a cannon standing in the doorway. Defeat him using stealth from behind, then run back to the sculpture idol and rest. Repeat this as many times as desired. You can do approximately four runs per minute, resulting in over 12,000 sen and 70,000 XP every hour. Note: This trick was performed on an unpatched version of the game. It may eventually get patched. To avoid not being able to use this exploit, either do not install new patches before using this exploit or delete the patches. You can avoid patches being installed by disconnecting from the internet until you are ready for the game to install new patches.
There is a Demon Bell you can ring to make the game harder. It is currently unknown if there are any rewards connected to increasing the difficulty of the game. The bell is located at Senpou Temple, Mt. Kongo – Demon Bell's Temple. There is a Sculptor's Idol at the temple, allowing you to easily return at any time. The following are the two routes to reach the Demon Bell:
Early route: Aishina Outskirts, Outskirts Wall – At the stairway, past the General mini-boss, go right from the arena and take the cliffside path. At the Temple Posting note, grapple to the tree, then drop down onto the ledge below. This is a tricky jump that leads to a large cave entrance. The cave contains the Headless mini-boss. Jump down into the dark arena, and run across to a smaller cave passage with a secret wall. Lean against the wall to enter the Demon Bell's Temple.
Normal route: Senpou Temple, Mt. Kongo – At Shugendo, before the Armored Warrior, use the cliffs and follow the path up. It is to the left of the Armored Warrior boss bridge. Drop down and take the secret bridge along the cliffs. You will need to make a tricky jump —- the bridge is located below the area with the red and white pinwheel. This path leads to the white pinwheel.
To activate the Demon Bell, approach it and inspect the bell, then use the ringing mechanism. You will gain an item and an effect. You can disable the Hard difficulty with the item in your inventory, allowing you to return to the Normal difficulty. In Hard mode, enemies are harder to defeat and inflict more damage, but they also drop better loot.
In New Game+, you will get the Kuro's Charm item early in the game, when collecting the Ornamental Letter. After meeting Lord Kuro in the tower and gaining your primary sword, you will have the option to give away Kuro's Charm. Give it away to increase the difficulty by adding chip damage to all blocks. You will also gain the benefit of approximately 17% additional money and XP. To reverse this effect, talk to the Old Sculptor to regain Kuro's Charm. However, you will not be able to increase the difficulty again until another New Game+.
Secret Great Serpent boss fight:
The location of this boss fight is Senpou Temple Mt. Kongo area, Senpou Temple Mt. Kongo idol. This boss fight is only possible after unlocking the "Puppeteer" Ninjutsu by defeating the Folding Screen Monkeys boss at the end of the Senpou Temple Mt. Kongo region. You must also have progressed through the Sunken Valley region to make the Great Serpent available to kill. Then, go to the Senpou Mt. Kongo idol (first one in that region). From there, drop down the cliff to the right to see a single enemy standing by a lever with a kite attached. Backstab this enemy and use the Puppeteer skill on him. He will then use the lever to move the kite and hold it in place. Next, go through the monk forest, through the prayer room, and to the next area where a large tree is on the right side. From that tree, you can grapple the kite and fly to the other area. Then, drop down the platforms and grapple tree branches as you fall, until you reach the Sunken Valley Cavern idol. From there, you will reach a dead-end where where you can balance on a wooden beam and the snake will be below you, but only if you have already advanced through the Sunken Valley region. To defeat the Great Serpent, simply drop down on the Great Serpent's head from the path you had followed above to execute it. There is no actual fight, as it will instantly die. The reward for defeating the Great Serpent is the Fresh Serpent Viscera (key item) and "Great Serpent" trophy.
Easy General Naomori Kawarada boss fight:
The location of this boss fight is Ashina Outskirts - Outskirts Wall Gate Path. Immediately after this sculptor's idol, you will encounter a big samurai. He is the only enemy in the courtyard. To defeat him, sneak above the rooftops on the left, without being seen by General Naomori. Then, sneak up to him from behind and stab him in the back to immediately take away one of his lives. Next, simply attack with the standard sword attacks (R1), and whenever he attacks simply block (or counter by pressing Block (L1) just before his attacks land). Blocking is less risky though. After he finishes an attack, chain attack him again. Repeat this until his guard breaks to defeat him. Also, remember you have a revive and can restore health. The reward for defeating General Naomori Kawarada is Prayer Bead and Gourd Seed.
Easy Chained Ogre boss fight:
The location of this boss fight is Ashina Outskirts - Outskirts Wall Stairway. Immediately after this sculptor's idol, you will see the Chained Ogre upstairs. First, kill all of the smaller enemies in the area. Before going upstairs to fight the Chained Ogre, defeat the two guards at the bottom of the stairs. After going upstairs, go around the left corner to kill the enemy with a spear. You will now only have to fight the ogre. When the ogre attacks, press Left Analog-stick Up and dodge twice to get behind the ogre where he cannot hit you. Land two to three hits and repeat. Use this strategy to defeat the ogre without taking a single hit. The reward for defeating the Chained Ogre is Prayer Bead and Shinobi Medicine Rank 1.
Easy General Tenzen Yamauchi boss fight:
The location of this boss fight is Ashina Outskirts - Outskirts Wall Stairway. In the next area after the Chained Ogre boss is the General Tenzen Yamauchi boss. Ignore the boss at first and just kill all of the smaller enemies in the area. Try not to lose too much health. After the smaller enemies have been defeated, go back the way you came and escape the boss's sight. Then, return and sneak behind his back and attack from behind to instantly take one of his lives. When the boss attacks, press Left Analog-stick Up and dodge twice to get behind the boss where he cannot hit you. Land two to three hits and repeat until his defense breaks. If you killed the first boss, Naomori, you will have gotten a Gourd Seed from him. Another one can be found in the building after the Chained Ogre. Use these two seeds to upgrade the healing gourd (health flask) twice so you have three heals. The reward for defeating the General Tenzen Yamauchi is Prayer Bead.
Easy Gyoubu Oniwa boss fight:
The location of this boss fight is Ashina Outskirts - Ashina Castle Gate Fortress. After the previous boss, General Tenzen Yamauchi, you must drop down a cliff (where a tree is facing a large gap to the other side). After dropping down, you will reach a canyon where a big snake attacks you. Proceed through this area and follow the main path until you reach a battleground where Gyoubu Oniwa comes riding on his horse through a gate. Gyoubu is the first real "main boss" in the game. He rides on a horse and attacks with a spear. His strength is his long reach, but his weakness is his poor defense. As with any big boss, first learn to block all attacks; do one test run and just block everything without even worrying about attacking. When you got the attack pattern memorized, you can start. The easiest way is to block his chain attacks until he performs a heavy attack that leaves him defenseless for 2-3 seconds. Then, attack him twice. Immediately start blocking again (or if your posture is about to break), dodge back 2-3 times to get away and take a moment to let the posture recharge. Just block all of his attacks (do not counter, just hold [Block]) and always attack when he is unable to move. Repeat this process. It takes a while, but it is relatively riskless. Also, look out for when a green dot appears above Gyoubu's head. You can then grapple him with (L2). This will also temporarily make him unable to move for 2-3 seconds, allowing you to land a couple hits. Then, just block again. You could also keep your distance and let him ride around the area, then only use the grapple and attack twice, get away, wait for the next grapple opportunity, and repeat. This way you can always land two hits while keeping your distance. After taking his first life, he will start performing a sweep attack (red icon on screen). Jump (X) to avoid it. When you take his second life, press R1 again to execute him. The reward for defeating the Gyoubu Oniwa is Gyoubu Oniwa (Strength upgrade) and Mechanical Barrel (Prosthetic Tool upgrade).
Accomplish the indicated achievement to get the corresponding number of Gamerscore points:
Sekiro (70 points): All achievements have been unlocked.
Ashina Traveler (60 points): Traveled to all areas of the game.
Master of the Prosthetic (60 points): Upgraded all Prosthetic Tools to their limit.
All Prosthetic Tools (30 points): Acquired all Prosthetic Tools.
All Ninjutsu Techniques (30 points): Acquired all Ninjutsu Techniques.
Peak Physical Strength (30 points): Upgraded Vitality and Posture to their limit.
Ultimate Healing Gourd (30 points): Fully upgraded the "Healing Gourd".
Revered Blade (20 points): Received the "Kusabimaru" from Kuro.
Shinobi Prosthetic (20 points): Acquired the Shinobi Prosthetic.
Memorial Mob (20 points): Encountered the Memorial Mob.
Resurrection (20 points): Returned from the dead using "Resurrection" for the first time.
Additionally, there are 23 secret achievements:
Man Without Equal (60 points): Defeated all bosses.
Height of Technique (60 points): Acquired all skills.
Immortal Severance (30 points): Attained the "Immortal Severance" ending.
Purification (30 points): Attained the "Purification" ending.
Dragon's Homecoming (30 points): Attained the "Return" ending.
Shura (30 points): Attained the "Shura" ending.
Sword Saint, Isshin Ashina (30 points): Defeated "Sword Saint Isshin Ashina".
Master of the Arts (30 points): Grasped the inner mysteries of any combat style.
Lazuline Upgrade (30 points): Used Lapis Lazuli to upgrade any tool to its limit.
Gyoubu Masataka Oniwa (20 points): Defeated "Gyoubu Masataka Oniwa".
The Phantom Lady Butterfly (20 points): Defeated "Lady Butterfly".
Genichiro Ashina (20 points): Defeated "Genichiro Ashina".
Guardian Ape (20 points): Defeated the "Guardian Ape".
Guardian Ape Immortality Severed (20 points): Used the Mortal Blade to sever the Guardian Ape's undying.
Folding Screen Monkeys (20 points): Caught the Folding Screen Monkeys.
Great Shinobi - Owl (20 points): Defeated "Great Shinobi - Owl".
Father Surpassed (20 points): Defeated "Great Shinobi - Owl" at the Hirata Estate.
Corrupted Monk (20 points): Defeated the "Corrupted Monk".
Gracious Gift of Tears (20 points): Defeated the "Divine Dragon" and obtained the "Divine Dragon's Tears".
Isshin Ashina (20 points): Defeated "Isshin Ashina".
Demon of Hatred (20 points): Defeated the "Demon of Hatred".
Great Serpent (20 points): Defeated the "Great Serpent".
Great Colored Carp (20 points): Defeated the "Great Colored Carp".