Just use a Smeargle with Mean Look, False Swipe, Spore and Ingrain; catching them will be super easy! ;)
Since Gen II, there have been some legendary Pokémon in most of the games who roam around the region. This started with the legendary Dogs of Gold and Silver: Entei, Raikou, and Suicune. Once you encounter them in Ecruteak City’s Burned Tower, it’s possible to track their movements through the Johto region. In Crystal, as well as the remakes of Gold and Silver. Suicune is a stationary legendary.
Before I start hunting, I make sure I have about 30 high quality balls (I use Ultra Balls, Dusk Balls at night and Quick Balls — but only try those once in a while. Master Balls are good too, but where’s the fun in that?), and craft a team specifically for roaming capture: for me, it was Gloom* as a paralyser, Salamence* to do the heavy damage, Scyther with Technician ability for False Swipe, and Sableye* for Mean Look.
*Pokemon imported from Sapphire to SoulSilver
To elaborate, Gloom’s pretty obvious with Stun Spore, Salamence’s Headbutt took out just less than half each dog’s HP per hit, Scyther’s False Swipe gets a 1.5x power boost to 60 base power with Technician, so basically two Headbutts and one False Swipe leaves a Dog with 1HP; Sableye’s purpose was to use Mean Look to prevent them from fleeing, and its type combination gave it the added bonus of being immune to 2 of Raikou’s attacks, and one of Entei’s. Unfortunately this does not include Roar, so I still had to deal with that whenever they felt like it.
After assembling this team, I would go to Violet City and down to Route 32 (or any other joining route), check Pokégear, and repeat until one of them appears on your route. They will attempt to flee at the end of every turn, and even if you use Mean Look they can still use roar to get away. But anyway, for me, the order of events in battles with each dog was:
4) False Swipe
5) Mean Look; ultraballultraballultraballultraball
7) Repeat steps 5 and 6 until capture
And then there were tears of joy. This process took me hours. It also cost me about 50000 Pokédollars in balls.
I just used a Master Ball on the other roamer, Latios, so that he’d be matching the Latias I caught and imported from Sapphire. That Master Ball usage brings me to another interesting story- while playing Sapphire, I realised that the only runner was Latias, so I figured hey, why not Master Ball? Huge mistake. You’ll find out about that next week though.
Advice for other players: Master Ball a roamer if you feel you can handle the high-levelled stationary ones. Be aware of different kinds of balls and of how and when to use them effectively. Also make sure the sun is actually down before you start throwing Dusk Balls.