The chance of getting Gilgamesh on a 10 roll is 2.96% (as compared to 1.65% over 10 single rolls).
I know a lot of people will be rolling for Gilgamesh once the event goes live, thinking "hey, a 3 percent chance... I can do that! Gilgamesh will be mine!" However, as a proud recipient of E-rank luck, (semi) responsible individual (OK, not really), and redditor who fully expects a maelstrom of mixed joy and despair to inundate this sub a few days from now, here's the math taken just a bit further in order to really put things in perspective and hopefully allow you guys and girls to make informed choicespleasedon'thateme and make your bid for the King of Heroes with.
The chance of getting Gilgamesh on a 10 roll is 2.96% (as compared to 1.65% over 10 single rolls).
Therefore, the chance of not getting Gilgamesh on a 10 roll is 97.04%.
The chance of not getting Gilgamesh on two 10-roll tries (20 rolls) is 94.17%.
The chance of still not getting Gilgamesh after five 10-roll attempts (50 rolls) is 86.05%.
The chance of still having to enviously sift through Reddit posts of other users boasting how they got Gilgamesh on the second roll and weren't even trying for him, and still not getting Gilgamesh after ten 10-roll attempts (100 rolls) is 74.05%.
The chance of still having to enviously (and now quite saltily) sift through Reddit posts of how one guy rolled three Gilgameshes in one 10-roll gacha and is now stapling them to his previous two to upgrade to level 5 NP Gilgamesh while still not owning a Gilgamesh yourself after twenty 10-roll attempts (200 rolls) is 54.83%.
In fact it would require twenty-four 10-roll attempts at the gacha to even have roughly a 50-50 chance at landing at least one Gilgamesh.
So yeah, I just thought I'd put this out there. Not to step on anybody's dreams, but if you are going to engage in the methodical insanity of rolling until you get Gilgamesh, I figure you should at least know what you're getting into. That said, best of luck to each and every one of you Gil-lovers out there. I'm too much of a mongrel to appreciate the King of Heroes and will not be partaking in the gacha festivities, but may the worthy among you find your devotion rewarded by his presence.