Spend a spark and a few spell points to swap your entity for another one you control. This replaces having to banish your current entity and then summon another. This is a handy spell to deal with an occasional nuisance, I have no idea why it’s one of the most expensive in the guild to study.

The in game help reads:

No saving throw.
Casting time: 4 rounds.
Type of spell: neutral spell.
Affecting stats: int/wis.
Cast type: rift.
Spell point cost: 18.
Once a riftwalker has control over a number of different entities, he/she can
transform their existing entity into another entity type.
NOTE: solo kills will NOT register on the top kills plaques for 30 minutes
after using this spell.
Syntax: cast transform rift entity at <type/name>
This spell uses 1 rift spark.