At least a few, on EU2 we already thought it was a myth.
I walked there every day with a large group, none of them got one. The players are very disappointed because of this.
Was the dropchance of Prisma calculated after the other events?
On EU2 there are not so many players as on US3 for example, there was a big round daily with a maximum of 35 players.
The ladder could be run only once a day, unlike the other events, (Valentine Zone, Halloween Zone), there you could kill this boss several times a day to get a special mount.
It might have made more sense to use the normal Prisma for this.
So now many players are very sad that their effort has remained unrewarded.
Personally I think an extra reward for getting to and defeating EMP prisma is/was in order but considering it was a once a day activity with maximum difficulty the drop rate should have been better for the mount. In fact of all the EZ rare drop boxes this ones structure flat out rewards the fewest no. of players.
in my opinion the best structure would be to give a very low drop rate box to a more communal boss and give the EMP prisma one a better chance at dropping.