you can find regiice near the dewford town,surf northwest.
Regice is on Island Cave on Route 105.
you must trade him from either Pokemon ruby, sapphire, or emerald.
You can't get him in platinum. You have to transfer him from a Sapphire/Ruby/Emerald.
you can't. trade with someone who has a ruby, sapphire, or emerald version
regiice cant be caught in Pokemon diamond, it can in platinum version, how ever you can transfer a regiice from ruby, sapphire or emerald if you have 1, or there is the method of cheating in which i am against. cheats lead to glitches and unsolvable problems. u can only get the regi known as REGIGIGAS.
in a Nintendo event
you either need an action replay or you need to transfer them over from Pokemon ruby/sapphire
In Pokemon Ruby,You get Groudon,Rayquaza,Regiice,Regirock,Registeel and Latios.In Pokemon Sapphire You get Kyogre,Rayquaza,Regirock,Regiice,Registeel and Latias.If you get the Mystery event or Mystery gift,You can get the tickets to get Jirachi and Deoxys.Extra: In Emerald you can get ALL of those Pokemon (legendary Pokemon in Ruby and Sapphire).But if you get the Eon ticket from Mystery event or Mystery gift,You can go get Latios if you caught Latias and Latias if you caught Latios.(Only in emerald).
The only way is through migrating them from Pokémon Ruby, Sapphire or Emerald or by trading.
You can catch Groudon,Rayquaza,Latios,Deoxys,Celebi,Jirachi,regiice,regirock,registeel,and Mew
Pokemon ruby's version IS Pokemon ruby.
You cant find a shiny regice unless you have action replay