None, the soothe bell is only used to increase happiness of your Pokemon you don't need it to evolve a Pokemon that evolves from happiness though it is a good idea to use it if you have it.
i think the Pokemon that evolves into gyarados is magikarp. it evolves at level 20
its zangooze..
it evolves curtain thunder Pokemon
Gloom
In Generation III (Ruby, Sapphire, Emerald, Fire Red, Leaf Green), the only Pokemon that evolve with a Thunderstone are: Eevee, which evolves into Jolteon; and Pikachu, which evolves into Raichu.
it evolves into golduck
Lombre
It evolves at level 35. It evolves into Vibrava.
I believe Swinub evolves into Piloswine in Pokemon Ruby at level 33.
Yes, it does evolve in Pokemon Ruby. It evolves at lvl 42.
Skitty evolves into Delcatty through the use of a Moon Stone in Pokemon Ruby and Sapphire.
Aron evolves into Lairon at Level 27 in Pokémon Ruby.