Your porygon isn't bugged you just used it for a tribute to boost another pokemon you can see the x at the top of the card and the heart. A card can have up to 3 hearts.
Because of the x you cant do that mucht with your porygon like evolution or level up, but you can tribute another pokemon to your porygon so it will be back to normal. Maybe the picture helps
Before Tribute
Wow! Thank you very much! That was the issue with my card, oh man, I thought I had 2 "legendary" cards, but they were just atributed.
I believe it's only 1, because after it gets an "x" it no longer can be used for attribute material. The only thing I think attribute does is increase the health of the card, please correct me if I'm wrong, I wish there was a super detailed guide somewhere to understand those mechanics
You had a good question so i made a quick research for you maybe it helps.
There must be a intern multiplier wich will be increased with each heart at the top.
At 3 Hearts the multiplier is round about 1.4 so u can multiply atk/def/life with this 1.4 and can calculate how strong the pokemon will with 3 hearts.
The multiplier is not exactly 1.4 in this sheet maybe because of rounding stuff only the owner knows the truth.
