This is what i think about legendaries:
needed help so he created 
, Then 
, 
, 
created time
created space
created a parallel universe to keep ours stable
then created legendaries like:
who made plants and stuff(IMO)
who created bad dreams
who made good dreams (IMO)
and 
how made.....umm.....something
who made air
who made water
who made land
who made wishes and granted them
who came from outer space
who created 
, 
, 
who created 
, 
, 
who made 
, 
, 
who made human emotion
who made human willpower
who made human knowledge
And
and 
who made the sea temple(and possibally coral reef [ IMO ] )
Then...
purified 's water
made thunder in 's clouds
made volcanoes in 's land
who shaped the land
who froze water
who made minerals
who made lightning (not thunder) in 's and 's thunderclouds
who made snow from water
who made fire from..... somewhere
And fianally, the land was made and
made all the other pokemon
plus
has 's DNA , because made him,basically like a child