A lot of these effects could be achieved the with Draw Sprite Animation patch by Vesly. You can call specific effects from this patch via events.
Heres a tip: in some emulators, you can toggle individual sprite layers (I use VBA-m). And you can use this to extract certain sprites that you can’t find in the ROM. You could use this to get the sprite for Ninian’s Ice attack, as well as other effects.
The Thief/Assassin spawn effect can also be implemented with this. The graphics for it are in the repo, I believe.