you get to challenge him to a battle
you get beldum.
Nothing happens you just trade him and he leaves and you go on with your Pokemon journey
Nothing happens after you see him but, if you catch Latias, he'll see you again
You can't battle Steven in Pokemon HeartGold.
You can't battle Steven in Pokemon HeartGold.
you dont.
No you can't
You will. Just go and battle the elite 4 and he'll be the 5th you battle
he gives you beldum, a Pokemon from hoenn. you can't catch beldum from hoenn in jonto or kanto so don't refuse the offer!
You can't battle Steven in Pokemon SoulSilver or HeartGold.
You get it from Steven way later in the storyline
You get it as a gift from Steven later in the game