New Game + Progress

Decide how you want to reach Altus Plateau later in the game: A) With the two halves of the Dectus medallion, B) Through the Ruin-Strewn Precipice, accessible going north past the Bellum church, north of the path toward the Dectus Lift, C) By letting the Abductor Virgin at the bottom of Raya Lucaria telport you to Volcano Manor, and defeating the Abductor Virgin duo. (option A is the easiest one, option C is possibly the fastest one)
Find Lusat in the Sellia Hideaway and get the Stars of Ruin spell. He is behind a secret cave behind an illusory wall. To reach the entrance, start at the Church of the Plague site of grace and head north up the hill and straight under the wooden arch. Look to the North-East for a small graveyard with a single sorcerer enemy wielding a staff and a club. Behind the main headstone, along the cliffside, there's a secret door you can reveal by rolling or attacking it
Get one Seedbed Curse from Leyndell Royal Capital: After you exit the room with East Capital Rampart grace, continue south past the Oracle Envoys and into the building. Inside, head down the stairs and face west to take the elevator. After the elevator continue west into the next building. Climb up the ladder to your right and go up the stairs. On the highest floor you will find the Seedbed Curse on a corpse sitting in a chair
Get Seedbed Curse (until you get 5) from Volcano Manor: From Temple of Eiglay, proceed until you reach the teleporter to Rykard, Lord of Blasphemy, then go back into the building and up the stairs to find a fog door that requires a Stonesword Key. Carefully drop down in the dark room using the hanging cages. The item will be on a body that is sitting on a chair guarded by enemies. To the opposite side of the room there's a path leading back to the door in the Volcano Manor lobby that can now be opened
Get Seedbed Curse (until you get 5) from Elphael, Brace of the Haligtree: From the Prayer Room Grace, head forwards until the end of stairs with two crossbowman above you. Jump on to the arch to the right and hop on to the platform to the left with the Crimson Teardrop Scarab. To the left should be a room with a Cleanrot Knight and a chest containing Cleanrot Knight Finlay Ashes. Hop onto the arch to the north-west and follow it up to a balcony. Follow the balcony to its end and the item will be found on a body sitting in a chair above the ballistae and the Putrid Avatar
Get Seedbed Curse (until you get 5) from Elphael, Brace of the Haligtree: From the Prayer Room grace, keep heading forwards, going down every staircase you come across. Drop down and head towards the room with two Cleanrot Knights inside but instead of entering, jump over the railing to the right and drop down one level. Turn around, enter the dark room right under the railing and you will find it on a body that is sitting in a chair
Defeat the Lesser Ulcerated Tree Spirit in Elphael. To reach the mini-boss, go to the Drainage Channel site of grace, go west through the doorway, climb up the ladder at the end of the corridor, and go out the doorway on your right at the top. The mini-boss is at the landmass across the gap to the left. To reach it, go up the slope on the right and walk across the tree branch, heading southwest across the gap. You can cheese the mini-boss with ranged attacks from the top of the nearby trunk
Find Alexander in Farum Azula and beat him in a duel. He will reward you with with Alexander's Innards and Shard of Alexander. To reach him: from the Dragon Temple Lift grace (can be accessed by using two Stonesword Keys), go past the plaza full of undead up the flight of stairs, turn right and you'll see two square bracket shaped archways. Jump on the archway on the left (closest to the sleeping dragon) to get over to the other side. Alexander can be found directly on the flat arena after crossing the crumbling tower