The Blur

The Blur was a form of regeneration in which a Time Lord's appearance "quickly blurred and their new form appeared". (PROSE: How to be a Time Lord)

An example of this was the Third Doctor's regeneration into the Fourth Doctor. This regeneration was achieved with "a little push" from Cho-Je, who had shortly prior underwent a similar regeneration from K'anpo. (TV: Planet of the Spiders)