TryObjectEvent arbitrary code execution is an engine vulnerability or glitch, known to be in Pokémon Crystal.
When this function is called, if the carry flag is not set, it is possible for the game to cause arbitrary code execution with bc as the pointer.
The following is the code that causes it in the Pokémon Crystal disassembly. It seems the fix is to add a pop bc instruction.
-; Bug: If IsInArray returns nc, data at bc will be executed as code.
ld de, 3
ld hl, .pointers
jr nc, .nope
ld a, [hli]
ld h, [hl]
ld l, a
- ; pop bc
+ pop bc