Split-regeneration is the instance of one Time Lord regenerating into two different forms. This can be natural or forced, due to the circumstances.
- Gryphon, the first President of Gallifrey, may have had a split-regeneration in his second life, as he received visions of places he'd not recognized, although this has not been proven.
- Rassilon figured out the way to force a split-regeneration, and tried it on himself at one point in time, but this may have caused his slow ascension into madness.
- The Shalka and War Doctors were one split-regeneration. This may be due to the Eighth Doctor's temporary revival, though this wasn't proven.
- Split-regenerations can fail, as with Rassilon when he attempted it on his half-sister with alchemy, and she died three days later.
- One or both cats may have visions of what the other is doing. Or, in rare cases, neither of the two are aware of another.
Shalka and War Doctors.