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With a very happy grin on my face I can now report that I have made some definite progress with my five-boxing: I cleared Botanica in Heroic mode with my characters Stephanius, Captn, Alaire, Blaire and Dlaire.
After clearing the Steamvaults a couple of times, I went for other instances and cleared Mechanar, Botanica and Arcatraz as well as Shattered Halls several times each in normal mode. I spent considerable time in Botanica to practice, get Scryer tokens, Sha'tar rep and the Bangle of Endless Blessings for Captn.
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After responding to someone's desperate cry for a healer yesterday night, and ending up in a pug with an ill-equipped tank, I was painfully forced to acknowledge that the only thing holding my team back from doing heroics was myself. So I went for it. It took me a while and cost me half a dozen stupid wipes, but I bagged 25 badges in Botanica today.
I will defenitely now look out for the daily heroics, not just for the daily normal!
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On a pure eyecandy level, I have now started to use 'Parrot' with a little modification as suggested on the dual-boxing.com forums, showing my party's damage in the HUD, like shown here. Besides neat looks, this also organizes the combat log information into groups by type and time. Thereby AoE attacks show as one big number, even combined into one number if its a seed from each warlock, like in this screenshot.
Cheers, Steph.