Guild Wars 2

My guild has unlocked guild bounty and after doing it a few times I had some questions that I wanted to get some answers and (informed) opinions on. We are a medium sized guild with about 20-25 active members. We have only done the T1 bounty missions and we have only suceeded about 2/4 times. Mostly do to being unorganized. We are now looking for the more difficult bounties, before triggering the mission, but some of them have been very difficult to kill, I assume due to scaling. Has anyone noticed the most effecient group size per champ? At first I thought a 5 man party was good enough but they seem to be much more difficult than regular champs. Is this true or is it due to 10 ish ppl attacking one boss? I would also appreciate any tips/tricks you guys have found as far as killing the bounty. For instance half-baked kumali gains might when you attack and has a fire shield. You need to remove his stability without attacking in order to knock him back to get rid of the fire shield. This fight seemed soo impossible, but people were randomly attacking/zerging him. Organization seems very important!

NOTE: Please don’t turn this into a “guild missions are impossible for small guilds” thread. While trying to find relevant and helpfull information on bounties this was all I could find. I’m only interested in details on completing them and would appreciate staying on topic. Thank you and good luck!