4th Gen Giratina? (Platinum)

[Symphonic.x.Fantasia]

Does he, by chance, go back to the Distortion World if you kill him by accident? And don't the lake trio do that too?

 

[Dusknoirs]

No.
He'll appear in Turnback Cave after you beat the E4.

I dunno about the Lake Trio.

 

[SaiiKo]

you've only got one chance for the lake trio i think

 

[Myles]

In Platinum (and I think DP, but I'm not 100% sure) all legendary Pokemon will be reobtainable after being knocked out, if you beat the Elite Four again, including roaming legendaries.

 

[professor plum]

Use the help thread next time 8|