On Doctor Who, the process of regeneration for a Time Lord is a profound, excruciating transformation. Every cell of their being explodes with celestial energy, transforming their entire being. It's probably for the best though, considering that if every Time Lord kept a bit of their past self, they'd look like the nightmare above.
This delightful amalgamation comes from YouTuber Dave Clipson, who's updated his previous mashing-together of every actor to star as Doctor Who's titular Time Lord (including John Hurt as the un-numbered "War Doctor") to now incorporate the recently-arrived 13th Doctor, played by Jodie Whittaker.
The process Clipson goes through is honestly quite fascinating. First he creates a base face (say that out loud a few times, it's a delight) that takes blended pairs of each actor to play the Doctor in the classic era of the show and forms an amalgam.
When it comes to the now six actors who've portrayed the Doctor in the 21st century (merged down to three pairs), some blending jiggery-pokery has to be applied to get an even contribution among the Doctors — Clipson blends his 10th Doctor/11th Doctor hybrid with both the War/9 and 12/13 faces in different strengths, like a nightmarish crumb coat before the final frosting, so to speak.
The end result is, depending on your frame of reference, either a waking nightmare or Eddie Izzard at his peak. Or at the very least a good argument in favour of keeping Regeneration as a complete and total renewal rather than incorporating bodily bits and bobs from the Doctor's past.