This file is a resource file for a spell using effect 127 (summon monsters). When the spell is cast, a number of creatures listed in this file is summoned based on the power level defined in the effect.

In BG2EE we have (spirsumm.2da):

2DA V1.0
0
     RESREF
1    spirbear
2    spirwolf
3    spirsnak
4    spirlion