Please tell me if there is a such thing as the Giant Rayquaza's Statue..

I don't think there's such a thing as the Giant Rayquaza's Statue Mouth. But there's a Giant Seviper in the battle frontier. No it's not the same as ruby or sapphire. I only know how you get Beldum(if you call it a rare pokemon), latios/latias, Groudon, Kyogre, Rayquaza, Regice, Registeel and Regirock.

I don't think the giant rayquaza's statue mouth is real (it sounds made up by someone crazy) but the giant seviper is at the battle frontier, and it's called the battle pike.
Its like are and s but it does have the opportunitys to get deoxys, ho oh, Lugia and Mew via a nintendo event

Yeah, unless you go to a Nintendo event you won't really be able to get the old rare pokes, BUT if you have AR or GS and use warp codes to get to them you can, including Deoxys(he's the super speed variation in Emerald), Mew(!!), Ho-oh, And Lugia. And there's way cooler stuff than in R/S,one of my favorite new things is that all of the Pokemon are animated(when you look at their summary and when they go into battle) and the starters(in the final evolutiuon)glow their color and look really awesome!! It's alot of the same, but the differences make it worth it, I think. Wireless ability, catching both Groudon & Kyogre, picking Latios or Latis, alot of Jhoto Pokemon in the new Safari Zone section, the battle frontier, rebattling Gym Leaders, etc. It's cool. Check it out!

Enter the seviper thing is at battle frontier and you can get beldum latias latios Mew Lugia ho-oh deoxys and the legendary dogs via Pokemon colleseum