Currently the reason will return as UNKNOWN/DEFAULT as the new reason hasn't been implemented. Vanilla mechanic is that skeletons freeze and convert to strays.

Suggestion as to API/implementation. No commit credit is necessary as the code suggested is extremely generic, just wanting the change implemented.

In EntityTransformEvent.

/**

• When an entity freezes in powder snow and a new entity spawns.
  */
  FREEZE,

In CreatureSpawnEvent.

/**

• When a creature is spawned by another entity freezing.
  */
  FREEZE,

For implementation. In EntitySkeleton, around Line 89.

this.a(EntityTypes.STRAY, true, EntityTransformEvent.TransformReason.FREEZE, CreatureSpawnEvent.SpawnReason.FREEZE);