Evolution line
This is the full evolution tree of Porygon — every stage, every branch and the condition that leads to the next form. The line has 3 forms.
Start of the line
Stage 2
From Porygon
Trade with another player, holding Up Grade
#233
Porygon2
Stage 3
From Porygon2
Trade with another player, holding Dubious Disc
#474
Porygon-Z