Here is one of my old posts about how the Cow King Quest works
Its funny that after all this time people still dont know how this works. I play more D2C then LOD but even there you find so many people that seem to mess this up all the time. Even with the changes to how it works in 1.10 vs 1.09
Here is some info on how on how it works in 1.10
You need the leg from that lev of game. If the leg is from a different lev game then it will look red and wont work.
To make the red portal you have to have killed Diablo in that lev game.
To enter the red portal you can be any lev and dont need to killed Diablo in that lev game. (that changed from 1.09)
To take a party members TP (blue) you need to kill Diablo in that lev game.
Low levs chars get next to no exp in any cow game untill they get to the mid 20's
High levs get very little exp in hell cows after they hit mid 80's If you have a good 8 person party you could still lev there at 87-88 but you could lev faster doing river/cs games.
KILLING the KING: in 1.10 (cow king quest)
The key to this is the char that gets the last hit on the king (killing blow) and if that char can still make the red tp or not.
If that char can still make the red portal then everyone thats down in the cow lev will lose the "cow king quest" IF THEY ARE IN THE PARTY OR NOT
If the char that gets the last hit on the king CANT make the red tp then everyone is safe.(then have killed the king for the quest in a different game, were in the cow lev when the king was killed someone doing the quest or havent killed diablo in tha lev game)
Now if you take a char that hasn't killed Diablo in that lev game (they cant make the tp) that char can kill the cow kill all they want and not lose the quest.
If you have a lev 60 char that just started hell and is only in act1. They have not killed hell Diablo so they can't make the red tp, so it is safe for them to kill the king all they want untill that char does kill hell diablo. Then its no longer safe for them to kill the cow king. That works as long as they never are in a game where someone else kills the king for the quest.
NOTE: when the king is killed by someone for the quest he will always drop 8 stamina pots
The only safe place to be when the king is killed is in town or back in chat.