I think a Riddle is terribly appropriate for a Harry Potter reference. And somebody has to get jump in and get their feet wet, so here goes:
Although Lord Strange and the quintuplets were
Lord Strange could be Lord Voldemort, or Bellatrix Lestrange, or her husband, Rudolph Lestrange. But I'm going to guess it refers to both Lord Voldemort and his loyal servant, Bellatrix LeStrange. The quintuplets could be Luna, Ginny, Ron, Hermione, and Neville, the 5 of whom were captured by 5 Deatheaters while Harry (holding the prophecy) and Lucius Malfoy looked on, in the Battle of the Department of Mysteries. The number 5 could also refer to the 5th book in the series (Order of the Phoenix), in which the battle took place. Lord Strange is also a reference to an Elizabethan acting troupe, Lord Strange's Men, which brings in the concept of a live performance.
not near the boiling water when it splashed,
This seems to be alluding to the duel between Lord Voldemort/Tom Riddle and Dumbledore in the atrium of the Ministry of Magic headquarters building: Voldemort fought with fire, and Dumbledore with water. This could mean that the performance would involve a fire/water battle.
Lord Strange maintained a serious skald.
This is referring to Sirius (serious) Black's death. Sirius was killed (note the spelling of "scald" as "skald") by Bellatrix.
A seemingly random event indeed.
A flash mob appears to be a random event but is actually planned. Or perhaps it would appear to be a random event because the building would be disguised as something else - a regular London office building, for example.
Altogether, it sounds like a live performance of the Battle of the Department of Mysteries at the Ministry of Magic. I vaguely remember someone saying something about a possible Ministry of Magic show at some point in the future. Perhaps they're thinking of converting MIB or another property into the Ministry of Magic headquarters, with (perceived) underground access and a live show featuring scenes from Order of the Phoenix? The MoM headquarters are located in London, so MIB (or Disaster or Fear Factor) would seem to be an appropriate place to put it.