1
First of all it is Pokemon Platinum NOT Pokemon platnum. The best way I would is by using a master ball. but you can keep holding it off and about an hour later use a timer ball.
lvl 48
You could level your low level Regigigas up to level 100 by giving it EXP. SHARE and then beating the Elite Four a gazillion times, or you could cheat and make Regigigas level 100 when you catch it.
Regigigas does not ever evolve, in any edition of pokemon
Regigigas is in the bottom of the temple in Snowpint City to get to battle you you need the three regis and a low level Pokemon because regigigas apears at level 1
regigigas don't have a new form in Pokemon platinum REGIGIGAS IS LEVEL ONE!!!!!!!!!!!!
in pearl and diamond it is level 25. i believe platinum is the same
A Chimchar evolves into Monferno at Level 14 in Pokémon Platinum.
splash
Piplup evolves at level 16. But that might not be on all games though.
It's probably the same as in the other games -- that is to say, level 55.
If you already have the Regigigas from a different GBA game then you go to the Resort Area then go to route 208 and in a cave that's right by the enterance to go to St. Mountain.