This simple library allows custom level specific items by using higher bits from Game->Litems array (0x20, 0x40, 0x80 etc.)
This library features example script - Link`s awakening Stone Beak item and Hint Bird Statue FFC that displays message, when stone beak from the same level is inserted into statue.
Subescreens are jank-mcjunk. There is no way to render custom level specific items beyond default ones in subscreen.
Updated 03.12.2023 - Added support of rendering custom level specific items in subscreens. Bugfixed main functions. Best to repeat setup process from scratch.

1. Global script combining: Put UpdateSubscreenLitems() function between Waitdraw and Waitframe comaands inside main loop of Active global script.
2. Set up a sequence of tiles for each custom level specific item: 2 blank tiles and then item`s tile. Animation is not supported.
3. Set IC_LITEM for custom level specific item class. Default is Custom Item Class 5.
4. Import and compile the library. Assign 2 item scripts, global script and 1 FFC script. No libraries beyond std.zh needed.
Item setup
5. Set item class to one assigned in step 3.
6. Set tile to 3rd one in sequence from step 2.
7. Assign LevelItem or MagicLevelItem item script.
D0 - Litem ID. Must be a power of 2, or you will give Link multiple items at once.
D1 - Message string ID.
D2 - ID of tile used by item, from step 6. Scripts cannot access Item`s tile in 2.53 :-(
Subscreen setup
8. Create and place 1x1 tile block with tile assigned to leftmost blank tile from sequence in step 2 and CSet to one used by item.
9. Repeat steps 2 and 5-8 for each custom level specific item to be inclused in the quest.
LevelItem
//Item script that grants level specific items.
//D0 - Litem ID. Must be a power of 2, or you will give Link multiple level specific items at once.
//D1 - Message string ID.
//D2 - ID of tile used by item. Scripts cannot access Item`s tile in 2.53 :-(

MagicLevelItem
//Item script that grants level specific items for all levels.
//D0 - Litem ID. Must be a power of 2, or you will give Link multiple level specific items at once.
//D1 - Message string ID.
//D2 - ID of tile used by item. Scripts cannot access Item`s tile in 2.53 :-(

LAHintBirdStatue
//Link`s Awakening bird statue. If Link inserts stone beak from the same level, it displays message.
//Place at bird statue`s location.
//D0 - Message ID.