Many strategies are flying around, which one is better? It depends of many factors. The one I use with the clan is as follows...
1.- Start attacking Krofin normally... no BR, no activation, no special items, no nothing.
2.- Eventually Krofin HP will fall to 50%, at this point a shield will be raised for 30 seconds
3.- At least two theories comes here:
3a.- You have 30 sec to do certain amount of DAMAGE, if you fail then HP will replenish to 100%
3b.- You have 30 sec to do certain amount of HITS, if you fail then HP will replenish to 100%
4.- The strategy we use on the clan covers the 2 options mentioned before, and it is that right after Krofin raises the shield for 30 sec, that is the moment to do BR, activation of special skills, all items to increase attack, put on cloaks, etc... as this will produce both that the party do increased amount of DAMAGE and increased amount of HITS
5.- If done correctly you will break the shield before the 30 sec ends so you can finish killing Krofin normally, if for some reason you failed, just continue hitting and casting spells normally until everyone is ready to be activated and items ready to use again, wait again until HP goes 50% and the shield raises again and start the strategy again.
With this strategy we managed to kill Krofin almost always on the first try, except one or two occasions we did it on 3rd or 10th attempt because of just bad coordination.
Hope this help you