Riven FLST resources
They seem to specify which SFXE resource each card must use.
Each FLST resource is a list of records; it starts with an unsigned short record count, followed by that many records. The record size is 6 bytes:
|unsigned short||index||Record index, starting from 1|
|unsigned short||sfxe_id||Resource ID of the corresponding SFXE|
u0 is always zero. Changing it seems to have no effect.
FLST resources are very often empty (meaning no SFXE for that card) or with just one record.