grow = percentage to increase size by the end of life span.
1.0 is default, which grows to 2x size.  0.0 means it stays the same size.

This applies to Explo entities as well, for the individual puffs.

Gravity = amount of world gravity to apply to entity, default is 0.0, 1.0 is normal grav.
This applies for Explo entities as well.

RandomRotate = 0 to disable random rotation of the smoke sprites.

