I'll go ahead and announce this now:
Starting next round, Jirachi will be banned from this tour.
Jirachi was always one of the best Pokemon in UU every time it was allowed, thanks to near-perfect stats, a great typing and a fantastic movepool that gave it a ton of sets. Whether it was acting as one the best pivots and revenge killers in the game with its Scarf set or completely crapping on balance teams with its SubToxic set, it was always a major threat.
However, with the advent of Z-Happy Hour, Jirachi has crossed beyond the "really damned good" line. A boost to all stats combined with Jirachi's already formidable bulk and decent Speed makes it near-impossible to kill, and while it isn't an offensive powerhouse by any means, Iron Head's 60% flinch chance and enough coverage to break through any possible counters makes the set extraordinarily hard to play around.
Jirachi will still be allowed for any remaining games this round, but will be banned from round 4 and beyond.