Card Size is Different Paper Quality difference and Paper Thickness, but this depends on the set too I think, because they may change the paper stock that they use depending on cost of materials you can also ask a Pokemon Professor, they may have insight into fake cards entering the market and be able to give you pointers in spotting fakes
From a personal perspective, Destruction and Chaos are the two factions that I find the hardest to play with, that demand more knowledge of you deck, knowledge of the typical traits of your opponent deck and just a higher skill level to play
Remember that Mega Evolutions function differently from other cards (including EX) in Pokmon TCG Pocket, and reflect the new rules set by the Mega Brave and Mega Symphonia sets in the physical TCG: Knocking out a Mega Evolution card rewards you with 3 points, granting you an instant win in TCG Pocket
Fan art in the US is protected under, among other things, 17 U.S
9 Cerulean Skyfire Grants Hamon a Spell/Trap Negate Structure Deck: Sacred Beasts Jul
The Wurm is susceptible to exile-based removal though, so watch out for that.