There are two methods that ET can be invoked — via direct summoning or by linked transference.
This process is used by mortals that have the ability to call into the Synthetic Domain. Through rituals, either discovered or documented, it allows for a person to become the host for a Lightbearer.
It requires manipulation of the Synth, and this calling is enough to demonstrate required will that the callee wishes to receive. However, one detail that is often left out of the process is that once the Lightbearer answers the call, the possession replaces the mind of the person indefinitely.
Once a Lightbearer is already possessing a mortal body, he can transfer himself to another. In order for this to be allowed, the Lightbearer must have direct physical contact with the intended target and must call upon the Synth. If either of these conditions are not met, the Lightbearer is forced to return to the Synthetic Domain.
When a Lightbearer is in possession of a host, the mind and memories of the mortal that existed prior are replaced entirely by the mental capacity of the Lightbearer.
It is also paramount that the Lightbearer attend to the natural well-being of the host. For example, the host still needs to be fed and watered. After possession has been completed, it may take a few moments for the Lightbearer to realise how to control breathing and other motor skills.
Should the host become deceased, the mortal body can no longer be controlled by the Lightbearer and is expelled from the mortal realm, returning to the Synthetic Domain. Additionally, under the Tournament rules, this is considered a loss to their game upon the Arena concerned.