On Hardmode Crota still seems to see invisible players about 1/3 of the time, knights shooting invisible players and tracking their movements. Croata's shields not going down, croata moving positions faster than normal...
Enrage also starts a lot earlier than before...
Also having the Deathsingers Song still going well into crota's fight is stupid.
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The enemies, with the exception of crota, 2 I'll continually strike the last spot they saw you and investigate it. I've gone invisible dozens of time and still be hit by enemies shots because they attack your last known location. Crota can "see" when your invisible but he is programmed not to strike you. When he does strike you it's most likely there was some sort of lag in the game where he got up later than you see but in accordance to the other teams view he may have already gotten up.