Dark Ember

The Dark Ember allows Andre to ascend a +5 divine weapon along the occult path. Occult weapons deal bonus damage against Gwyndolin and Gwyn. You should already have the Occult Club, collected from a chest at Anor Londo. Stick to that occult weapon. However, should you want to experiment with other occult weapons, then collect the Dark Ember from the Painted World of Ariamis. Use White Titanite Chunks to upgrade an occult weapon to +4. For now, farm White Titanite Chunks from the Pinwheel Servants. There is a better farming location, available after you have defeated Bed of Chaos, Four Kings, Gravelord Nito, and Seath the Scaleless. You will pick up a White Titanite Slab in the DLC and use the slab to fully upgrade an occult weapon.

Anor Londo

Start from the Darkmoon Tomb bonfire. Crank the lever of the spiral staircase so the mechanism goes as low as it could. Descend the staircase to reach an area filled with Painting Guardians. Defeat each enemy one at a time to allow you safe passage to the massive painting at the back of the room. Interact with the painting to be transported to a secret area.

Painted World of Ariamis

77. Painted World of Ariamis: cheese the Undead Dragon, Dark Souls: Remastered

78. Painted World of Ariamis: Large Titanite Shard, Dark Souls: Remastered

81. Location of Annex Key, Dark Souls: Remastered

82. Location of Dark Ember, Dark Souls: Remastered

Your objective is to collect the Annex Key to open a path leading to the Dark Ember. Collect other treasures in the area if you want such as Dragon Scale, Large Titanite Shard, and soul items. Get the Annex Key and collect the Dark Ember, then fight the area boss to unlock the passage out of the painting.

Crossbreed Priscilla (optional)

79. SL1 Crossbreed Priscilla, Dark Souls: Remastered

This boss is difficult due to her invisibility. Two-hand a Lightning Reinforced Club+5, enter the fog wall, and R2 her tail. Wait for Priscilla to become invisible. Bait her into walking along the snow-covered floor, thus leaving a trail of footsteps to allow you to figure out her position. Dash to her side or behind her (I know she is invisible but you can figure out whether you are in front or behind by looking at the position of her footsteps), get in an R1, and roll away. Deal enough damage to Priscilla and she would become visible again. Use the same strategy as before. Get behind Priscilla to allow you to safely attack her.

80. Fire Keeper Soul from Darkmoon Knightess, Dark Souls: Remastered

Defeat Priscilla and approach the cliff edge to initiate a cutscene. You will then be transported back to Anor Londo, in front of the massive painting. For an extra Fire Keeper Soul, you might want to defeat the Darkmoon Knightess at the Anor Londo bonfire. Find Andre and give him the Dark Ember.