Like most One Piece TCG cards, the value of Trafalgar Law depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Emperors in the New World)
In case there is none, the same mana investment can be used to transform an Incubator token while still getting the same replacement regardless
That includes all the Un sets, Portal and other Starter sets, and stuff like the Global Series, Secret Lairs, and more
Certain cards can succeed by relying on their specific strengths, or they can even function as their own engines without the use of Welder or Blacksmith
Note what lands and monsters in a Commander deck worked well and what didn't
I have also started to collect cards that feature Charmander in their artwork