The Divine Link and using the pet to "stop" the doppelganger's regeneration doesn't work (the pet does not stop the health regeneration animation, despite what people keep saying), and I even tried dolls to take advantage of the "attacking stopping health regeneration" which also didn't work.
Doppelganger - Auto regen actually stalls when it gets hit by anything - in order to have an easier time with this fight try to have and do the following: -Mana Shield (or really high defense) - a pet (your free thoroughbred works) - Rank 1 Divine link (Preferable)
Chain Crush doesn't stun the Doppelganger. Or rather, the stun indication thing will appear above its head, but it'll still act normally. I found that the skill animation for Chain Crush took a second or so longer to settle compared to Chain Impale during that fight, so I opted for Chain Impale instead. Here is what I did to beat the Doppelganger: I catered 10x Super Sticky Mochi gained from ...
The doppelganger, I actually don't even recall in g21. I had to actually look up where it was, probably because I shredded it that fast, and that was with a mediocre firebolt on a wimp connection. Which for this fight looking at the wiki, again, recommends Pet Link, and if the doppelganger uses shadow spirit, resetting its AI with windmill.
The instant regen of the doppelganger is game breaking. Even if I final hit with focued beam sabers in Champion mode it's still not enough to overcome that regen.
G12 and G11 did not make me waste tons of Soul Stones, and Doppelganger could be mitigated with a Royal Alchemists. It is also a bit of me doing the fight when it was just released, in the days where Wiki is heavily outdated.
Shadow Cast City is my go-to for up to 5. Doppelganger also spawns quite a few at the end.
As normal skills apparently couldn't reach it, I used Doppelganger to be able to attack it. As a result, I'm now stuck outside the normal area due to Doppelganger teleporting me beyond the invisible walls.
Doppelganger Skill Training Potion Luna Crystal Staff Appearance Scroll Andris Wing Staff Appearance Scroll Ladeca Short Sword Appearance Scroll Star Candy Mace Appearance Scroll Toy Hammer Appearance Scroll Smiley Knuckles Appearance Scroll Platinum Hammer of Durability Lucky Red Upgrade Stone Ring Torque (Enchant: Transparent/Tidal) (Reforge ...