You don't, so sorry and you wont get on in there but if you do...
you can't catch seviper on Pokemon ruby (Pokemon sapphire only)
Using action replay get the capture trainer Pokemon cheat and then an ace trainer near stark mtn has one
You need to trade seviper to firered from sapphire.
The only way is the Pal Park.
You can catch Seviper in Ruby, Sapphire, Emerald, HeartGold (IV), SoulSilver (IV), Black and White.
how do you catch a mewtwo on Pokemon platinum
you cannot catch the 3 regi's in Pokemon platinum you have to catch them in Pokemon emerald then transfer them to Pokemon platinum. thnx
season 7 ep 9
no Pokemon evolves into seviper
You can't actually catch him in Pokemon platinum but you can migrate him over to platinum if you have him in another game
you can't catch him in platinum but in soulsilver or heartgold you can catch him then trade it to platinum.
Seviper is a Poison type pokemon.