You get it get by not hoping on Dandelions horse ...
You move over to the first whorseson thugs, kill them of,f turn right to see the big closed gate, wait some seconds wil Dandelion lets it open for you, then hop on your WHITE HORSE and never leave it, before Dandelion screams az you, that you should leave it back near the end of the way, which means, you have to make with the horse some jumps over some barricades.
When Dandelion screams at you to leave back the horse, ride with it nearly to the spot, where dandelion left back his horse, hold circle, kill then off the few thugs that are nearby and move then through the door.
green check mark...
Had to do this twice also too, that fail mark seriously pissed me off, because its again such a retarded 100& optional task, because you can simple also doo all of the way to the goal also too without using even at all the horse and just slaighterign your way through, like I did it the first time, because its much more fun, due to the endless respawning enemies and Ciris sword in that mission having a real high chance to do critical instant killing hits that the body parts just fly in second tact lettign ciri look like a real brutal slaughterer in Kill Bill Style^^
So reload the save, did it again, used the stupid horse, never left it, ect. pp like described and job done perfect.
But there are usually tons more stupid quest qwith automatic fails to follow, the next one that puts be in frotn of a hard nut to crack currently is Redanias Most Wanted... that you receive shortly before or after that Ciri part from Radovid.
How I wish that CDPR would finally fix all quests by removing these braindead obsolete optional fail objectives by lettign them simply disappear instead of lettign them being shown as failed objectives... as if it would be such a great difference if you give a certain crystal in RMW to either Triss or Yenne,ver you will get to hear from both the same, you will see from both the same, it has absolutely no influence on the games story, unless you give it maybe to radovid, what would be an absurd thign to do anyway which would be I guess currently under CDPR's silly objective design most likely the only option to get that quest done without a fail mark,, but as I get to know CDPR by now, I thing Im even wrong with that and the quest ends with fail marks for simply both sorceresses then >.> /facepalm
