(I know SPDShadowRanger gave you guys the update, but I worked hard on this so I'm posting it anyway.
)
Some new tibits about Pokemon HeartGold and SoulSilver has been revealed in the newest trailer; this time bringing back an old feature, confirming hints of Pokemon Crystal elements are in the game, a few more Gym Leader things. So let's get onto the picture shall we?
Attacking Trees Were Never So Productive:
In Generation II, the attack Headbutt got a new use: You could use it to Headbutt trees. By doing so, you might have a Pokemon fall out of the tree and then engage it in battle. While most of the time you'll probably battle with a Caterpie or Spearow, there were 4 Pokemon you could only get from Headbutting Trees: Exeggcute (Common), Aipom (Uncommon), Pineco (Rare), and Heracross (Rare). Now while only a small pool of Pokemon learned Headbutt through leveling up, it was made into a TM, TM02, to solve this accessibility problem and MANY Pokemon were able to learn the TM02. But you couldn't just go around headbutting any tree you saw, but rather only small trees (trees that were as big as your character sprite). However this feature came and went much like other features in Generation II, and though this concept was forgot about in Generation III, the Generation IV Sinnoh games introduced Honey which could be smathered onto gold trees to attract Pokemon to it and thus have the player battle attracted Pokemon.
However, this long forgotten feature has just been revived! In HeartGold and SoulSilver you can once again Headbutt trees, but this time you can look to do it on any tree you can reach! But this bears questions such as will there be no Honey? Will Zen Headbutt also be used in the same way?
FUN FACT: If you look through the coding for Pokemon Gold and Silver, you'll find an item called Sweet Honey indicating the Honey smathering feature might have been intended to be used but it was scrapped and replaced with Headbutting Trees and the move Sweet Scent to attract Wild Pokemon.

(Being a Fire-type, Entei shows its dislike for trees but headbutting them, though why it just doesn't burn it no one knows.)
I See You, Suicune:
In Pokemon Crystal, Suicune played a bit of a more importent role in the storyline than its two other fellow trio members, occasionally appearing in front of the player and soon running off. After this happens you'll also have an encounter with Eusine, and eventually Eusine will battle you in hopes of getting Suicune's respect. However Suicune seems to be only interested in you, and thus became the only member of its trio to be a stationary Legendary rather than a roaming Legendary who knows the move Roar.
But while Eusine was confirmed to be in HeartGold and SoulSilver and we saw all three of the Beast Trio in a screenshot of the Burnt Tower's basement, it wasn't until this picture if Suicune appears in front of the player at certain points of the storyline. But now we know it will, but whether it'll be the only member of its trio to do so or if it'll be a stationary Legendary like it became in Crystal still remains to be unseen.

(Suicune likes to take strolls in grassy areas which have no purpose in the game rather then to just have a cutscene showing it in the grassy area where it soon runs off from.)
No Fancy Redecorating Can Hide You Didn't Change The Gym Puzzle:
We all know that the first Gyms in Kanto, Hoenn, and Sinnoh have a lot in common: They are Rock-type, the trainers in those gyms are skipable, all their Pokemon or over level 10, and there is no puzzle to figure out. But for Johto only the very last part is true. In Generation II the first Gym Leader you'll be facing is Falkner, a Flying-type Gym Leader who's Gym requires you to battle two trainers before battling him. But when you do finally battle Falkner you'll discover his highest level Pokemon is his Pidgeotto at level 9, thus making him the weakest and easiest Gym Leader of any Generation.
But with HeartGold and SoulSilver Falkner has a chance to redeem himself, unless he spent too much time on redecorating the Violet City Gym. The new Violet City Gym is now a hanging platform over a bottomless pit being held up by a single support beam (I guess it isn't bottomless then...) with rotating gears. However beyond that the Gym is rather the same, or is it? If you look closely (okay, not really), you'll notice on each side there is an semi-invisible pathway which could take the player from the start of the Gym to either the middle or all the way to the Gym Leader Falkner! And that's all I really have to say about this gym, though I do hope they up Falkner's game a bit, I mean in Generation II he only had a level 7 Pidgey and Level 9 Pidgeotto. I think he should have 3 Pokemon or at least give him a Generation II Pokemon like Hoothoot or Skarmory!
FUN FACT: A level 9 Pidgeot? But Pidgey evolve into Pidgeotto at level 16, HE'S A HAXOR! Well, not quite. While it's true Pidgey evolve to Pidgeotto at level 16, in Pokemon Yellow you can catch a Pidgeotto at level 9 to match Ash catching a Pidgeotto early in the anime. Okay, that's all and good, but Pokemon Yellow is Generation I while Falkner is a Generation II Gym Leader. Well guess what, you can also catch a Pidgeotto at level 7 on Route 2 in Gold and Silver.

(Vertigo, acrophobia, ornithophobia, aerophobia... if you have ANY of these, even one, this gym might have you screaming.)
One last note, we finally get our first screenshot of a Gym Leader's battle sprite and its none other than Jasmine. I already went over her whole deal so we'll skip that part. Anyway she looks to be now wearing a blue dress instead of a white one (but that could be because of low picture quality) and still has 3 Pokemon. But are they still two level 30 Magnemite (which should have evolved into Magneton by now) and a Steelix is unknown. However, though she's a little better then Falkner, but being the 6th Gym Leader she should have 4 Pokemon. If not that at least evolve one of her Magnemite into a Magneton and/or give her another Steel-type that was introduced in Generation II like Scizor, Forretress, or Skarmory. You could even have her Ampharos, Amphy, join in the battle!
Seriously though, what is wrong with the Johto Gym Leader's Pokemon? They either forgot they were Johto Gym Leaders, what position they were, what levels their Pokemon evolve at, have too many duplicates of one of thier Pokemon, or a combination of these things! Let's go over each Johto Gym Leader, shall we?
Falkner: Just went over him above, he seemed to forgot he was a Johto Gym Leader and is also having a little trouble raising his team. With a level 7 Pidgey and Level 9 Pidgeotto, he can do better. First upgrade his Pokemon so they'll be over level 10 (12 and 14 seem to be popular levels for first Gym Leaders), and have him use at least one Generation II Pokemon (Hoothoot would be nice, maybe even a Murkrow or Skarmory, or throw a curveball and give him a Ledyba, Natu, Hoppip, Yanma, Gligar, Delibird, Mantine, Togetic, you see where I'm getting at here?).
Bugsy: Another case of forgetting he was a Johto Gym Leader as well as remembering Merapod and Kakuna both evolve to Butterfree and Beedrill, respectively, at level 10. He has a level 14 Metapod, level 14 Kakuna, and level 16 Scyther. First off, EVOLVE YOUR METAPOD AND KAKUNA TO BUTTERFREE AND BEEDRILL, respectively! Oh, and I checked and found that Scyther can evolve to Scizor at pretty much any level so you might as well evolve that too! You may also want to think about these following Generation II Bug-type Pokemon: Pineco, Ledyba, Spinarak, Yanma, Shuckle, and Heracross.
Whitney: She seemed to have forgotten what position she's and thinks she is the first Gym Leader having two Pokemon even though the Gym Leader before her, Bugsy, has three. These two Pokemon of her are a level 18 Clefairy and a level 20 Miltank. Now beside she should get going to Mt. Moon to get a Moon Stone to evolve Clefairy into Clefable, the only complaint I have here is that she should get a third Pokemon. And this a wide selection of Normal-type Pokemon to choose from (Furret, Togetic, Aipom, Dunsparce, Snubbull, Teddiursa, Porygon2, Stantler, Smeargle, Blissey, Noctowl, and Girafarig), she just needs to get one and she'll be set.
Morty: Forgot he was a Johto Gym Leader and has a double. Making Morty's team is a level 21 Gastly, level 21 Haunter, level 23 Haunter, and level 25 Gengar. Like with Falkner Pidgeotto, you can catch Haunters at lower levels (lowest I can find is 17) so I'll let this one slide (incase you were wondering, Gastly evolve into Haunters at level 25). Anyway you must forgive Morty a bit here, the only new Ghost-tye they introduced in Generation II was Misdreavus, but the least they could do is replace one of his Haunters with a Misdreavus! Morty, replace one of your Haunters with a Misdreavus, and you got my thumbs up.
Chuck: Forgot he was a Johto Gym Leader and also thinks he too is the first Gym Leader only having two Pokemon while the Gym Leader before him, Morty, has four! Chuck has a level 27 Primeape and a level 30 Poliwrath. Now I'll like to note in the anime Chuck does have a Machoke however being Chuck doesn't have any Generation II Pokemon I'm gonna skip it (although if I were to include it, I would say it should be a Machamp). Anyway, Chuck, here are two Generation II Fighting-types which I think would be appropriate for you: Hitmontop and Heracross. Pick one, or since you the Gym Leader behind you has 4 Pokemon, pick both and let the battles commence!
Jasmine: She seemed to have forgotten what level her Pokemon evolve at, she has a double, and might also be confused at what position she is. Having two exactly the same level 30 Magnemite and and a level 35 Steelix, she needs, like so many other Johto Gym Leaders, need a bit of help. For one thing evolve one of your Magnemite into a Magneton, get rid of the other Magnemite, and (being it was confirmed you still only have 3 Pokemon) replace it with one of these Generation II Steel-types: Skarmory, Forretress, or Scizor.
Pryce: Isn't to bad but might have forgotten what position he is. He has a level 27 Seel, level 29 Dewgong, and a level 31 Piloswine. Compared with Jasmine's Pokemon levels, Pryce needs to train up his Pokemon a bit as the 7th Gym Leader shouldn't have Pokemon who's levels are lower then the 6th Gym Leader's Pokemon. Likewise I would like to know where he got his Dewgong being Seel don't evolve until level 34 and I can't find anywhere you could catch a Dewgong below that level! Infact, his Piloswine is also under the evolution level as Swinub evolve into Piloswine at level 33! Anyway Pryce needs to raise up his Pokemon, get rid of that Seel (he has a Dewgong, he doesn't need its pre-evolution or another one), and her himself one or two of these cool Generation II Ice-types: Delibird and/or Sneasel.
Clair: Her main problem is just with having multiple of the same kind of Pokemon as well as maybe not knowing what position she is. She has not two, but THREE level 37 Dragonair (with only one of their moves being different) and a level 40 Kingdra. Now like Morty, you must forgive Clair as they only released Kingdra as the only new Dragon-type in Generation II, but still, THREE Dragonair?!?! They could have pulled a Lance and give her a Gyarados (they gave her one in the anime!) and an Aerodactyl. How about giving her a Charizard to handle those pesky Ice-types tormenting her Dragons, or maybe even a Tyranitar just cause its looks like a Dragon. Give her any other two (or three if they allowed her to have five Pokemon) Dragon-looking Pokemon so she doesn't wind up having THREE Dragonair!
Now I know what you're thinking "Aren't you being a bit too picky? If you look at other Generations you'll also notice that Gym Leaders use multiple of the same Pokemon or have the same number of Pokemon at the position the Johto Gym Leader is at". Now while I am being a bit picky, you do have to agree that at least for some of the Johto Gym Leaders have a problem with their Pokemon team.
How where was I? Oh, yay, the HeartGold and SoulSilver updates!

(Jasmine: *sniff* YOUR MEAN!
Me: Well sorry to tell you the cold, hard truth. Get different Steel-type Pokemon and maybe I'll feel different.
Jasmine: Okay then, how about this! GO DIALGA! *Dialga appears*
Me: WHA!?!? WHE-WHERE DID YOU GET A DIALGA!
Jasmine: Remember when Arceus allowd you to catch Dialga, Palkia, or Giratina and you chose to get Giratina?
Me: So Dialga went to you? Then who has Palkia?
Clair: *petting Palkia* You'll make a nice replacement for one of my Dragonair which people been complaining I have too many of.)
I See You:
Nothing more really to say with this new update, here is another pic I found interesting. Serebii says it's a Lookout Station (those buildings that connect certain routes together) but to me it looks more like the rooftop of the Goldenrod Department Store. You can decide what it is for yourself or, you know, wait till the game comes out when we'll officially find out then.

(I'm Sorry, but the depressed Sinnoh Electric-type Gym Leader is in another place with binoculars.)
Well, that's all I got till next update!