From Worlds Collide Wiki - Final Fantasy VI Randomizer
Chest Item Tiers

There are a total of 236 chests containing items and 7 chests containing GP. GP values are chosen using a triangular distribution between 1 and 65535. Items are divided into tiers I through S. Each chest randomly selects a tier using corresponding weights. For tiers I through A items are selected using a uniform distribution. Items in tier S each have their own individual weight.

As examples,
8.5% of the 236 chests will contain an item randomly selected from tier A using a uniform distribution. Therefore, each seed will contain an average of 0.085 * 236 = 20.06 tier A items and each item in tier A will have an 8.5 / 25 = 0.34 percent chance of being in each chest.

0.5% of the 236 chests will contain an item from tier S. Of those, 10% will contain a Valiant Knife and 2% will contain a Paladin Shield. Therefore, each seed will contain an average of 0.005 * 236 = 1.18 tier S items, 0.005 * 0.10 * 236 = 0.118 Valiant Knives (~1 in 8 seeds) and 0.005 * 0.02 * 236 = 0.0236 Paladin Shields (~1 in 42 seeds).

Tier I H G F E
Weight 0.10 0.12 0.03 0.015 0.005
Size 10 7 2 2 1
Avg. Per Game 23.6 28.32 7.08 3.54 1.18
Antidote Ether X-Ether Dried Meat Megalixir
Echo Screen Fenix Down X-Potion Elixir
Eyedrop Remedy
Green Cherry Sleeping Bag
Magicite Smoke Bomb
Potion Tent
Revivify Warp Stone
Tier D C B A S
Weight 0.09 0.25 0.30 0.085 0.005
Size 64 86 45 25 12
Avg. Per Game 21.24 59 70.8 20.06 1.18
Air Lancet Amulet Air Anchor Aegis Shld Cat Hood
Ashura Atma Weapon Assassin Aura Lance Exp. Egg
Bandana Aura Atlas Armlet BehemothSuit Fixed Dice
Barrier Ring AutoCrossbow Blizzard Orb Dragon Horn Gem Box
Blossom Back Guard Chain Saw Economizer Illumina
Buckler Bard's Hat Charm Bangle Enhancer Marvel Shoes
Cards Beads Circlet Flame Shld Minerva
Chocobo Brsh Beret Czarina Gown Force Armor Offering
Cotton Robe Bio Blaster Doom Darts Genji Armor Paladin Shld
Cure Ring Black Belt DragoonBoots Genji Glove Ragnarok
Czarina Ring Blizzard Drill Genji Helmet Snow Muffler
Darts Bolt Edge Earrings Genji Shld ValiantKnife
DaVinci Brsh Bone Club Excalibur Hero Ring
Dirk Boomerang Fire Rod Ice Shld
Epee Break Blade Force Shld Magus Rod
Fairy Ring Cherub Down Gold Hairpin Merit Award
Forged Chocobo Suit Graedus Moogle Charm
Goggles Coin Toss Hawk Eye Muscle Belt
Gold Armor Coronet Ice Rod Nutkin Suit
Gold Helmet Crystal Imp Halberd Pearl Lance
Gold Shld Crystal Helm Imp's Armor Pearl Rod
Hair Band Crystal Mail Man Eater Ribbon
Hardened Crystal Orb Memento Ring Sniper
Head Band Crystal Shld Mirage Vest Super Ball
Heavy Shld Cursed Ring Moogle Suit Thunder Shld
Imperial Dark Gear Mystery Veil
Iron Armor Dark Hood Oath Veil
Iron Helmet Debilitator Pod Bracelet
Jewel Ring Diamond Helm Rage Ring
Kaiser Diamond Shld Red Cap
Kodachi Diamond Vest Red Jacket
Kotetsu DiamondArmor Safety Bit
Kung Fu Suit Dice Scimitar
Leather Hat Dragon Claw Sky Render
LeatherArmor Drainer Striker
MetalKnuckle FakeMustache Stunner
Mithril Claw Falchion SwordBreaker
Mithril Helm Fire Knuckle Tack Star
Mithril Mail Fire Skean Tao Robe
Mithril Pike Flail Tempest
Mithril Rod Flame Sabre Thunder Rod
Mithril Shld Flash Tiger Fangs
Mithril Vest Full Moon TortoiseShld
MithrilBlade Gaia Gear Wall Ring
MithrilGlove Gale Hairpin Wing Edge
MithrilKnife Gauntlet
Murasame Gold Lance
Ninja Gear Gravity Rod
Plumed Hat Green Beret
Poison Claw Guard Ring
Power Sash Guardian
RegalCutlass Heal Rod
Relic Ring Hyper Wrist
Rename Card Inviz Edge
Shuriken Light Robe
Silk Robe Magical Brsh
Sneak Ring Magus Hat
Sniper Sight Morning Star
Sprint Shoes Ninja Star
Star Pendant NoiseBlaster
Stout Spear Ogre Nix
Tiger Mask Partisan
Tintinabar Peace Ring
Trident Poison Rod
Rainbow Brsh
Regal Crown
Rising Sun
Rune Edge
Shadow Edge
Soul Sabre
Tabby Suit
Thief Glove
True Knight
Water Edge
White Cape
White Dress
Zephyr Cape

Tier S item weights:

Item Weight
Marvel Shoes 0.15
Cat Hood 0.12
Snow Muffler 0.12
Gem Box 0.10
ValiantKnife 0.08
Fixed Dice 0.08
Offering 0.08
Ragnarok 0.07
Minerva 0.07
Exp. Egg 0.06
Illumina 0.05
Paladin Shld 0.02

NOTE: The cursed shield is excluded from all tiers and will not appear in chests.