I was bot lane as kog and shaco killed me, it gave him a double kill when I died. I dont know if this is known yet but could be a real game breaker

not really, its quite a hard thing to do. after scanning the forums, i seem to have found the MOST LIKELY cause of how it happens; Shaco's clone kills you. Unless you can describe any other things that were out of the ordinary, or say that he DIDN'T ult, then i think my research is done

http://na.leagueoflegends.com/board/showthread.php?t=1393783

adding to my list

the bug is caused if kogmaw's passive kills shaco's hallucination. Not 100% sure if shaco gets the gold for this or not but the scores are affected

I am easily able to fix the one with Shaco's clone killing Kog'Maw, but apparently there is at least one other one sneaking around out there somewhere. If you have seen any instances that do NOT involve Shaco's clone killing Kog'maw, and getting 2 deaths, please try to list any information you have, such as:

Enemy team's champions and who got the double kill
Your items
Killer's items
Applicable buffs/etc used/had (examples Lizard, Nashor, etc)

Description of the double kill - how it occurred. So far there are 3 known issues of how this can bug:
1) Champion with 'zombie mode' effect (Kog'maw, Karthus, or anyone with Yorick ult on them) dies and then immediately dies again, never going into the zombie mode effect. Seems to be only seen on Yorick as far as I know. I have a fix for this version of the bug, provided it only exists on Yorick.
2) Champion with 'zombie mode' effect dies and then somehow dies again right at the end. Seen a screenshot in another thread of Karthus killing a zombie Kog'maw at the end. Have no repro information for this version of the bug.
2) Champion with 'zombie mode' effect dies, goes into the effect of their zombie mode, and then at the end dies again. Easily reproducable with Shaco, but might also occur with Brand. Do have a fix for the Shaco bug. If you have any information about Brand killing Kog'Maw in this way, please give any information you have.

I got doubled kill by Shaco with red buff and nashors toothzx

Something very similar to this happened to my friend. He posted a video of it on youtube:

http://www.youtube.com/watch?v=_tqsdzTPCpA

I'll trust you can see his items and team, considering the video is HD. Brand is the one getting the double kill (with his ult) and his items are visible at 0:20. Gangplank gets the 2 assists, if that's relevant, and his items can be seen at 0:23. Enemy team has GP, Brand, Soraka, Riven, and one other not distinguishable in the video. Raise Morale is the only buff present on either Brand or Gangplank when the single/double kill occurs.

Edit: I looked through my LoLReplay files until I found the game. The 5th player on the enemy team is Akali.

bump for awesome information on brand's repro

On Saintvicious' stream, he got a double kill as soon as he killed Karthus as Blitzcrank.

Just like to pipe in saying I saw Kogmaw get double killed on Dominion. Can't remember the details surrounding it all but I thought that fact it happens on Dominion maps too is worth mentioning. I'll see if I have a replay for the game.