Pokémon Trading Card Game (GBC) Card Pop

[IngeniousDefault]

Hey there.

The US version of the TCG was already decompiled a while ago (https://github.com/pret/poketcg/blob/master/src/engine/link/card_pop.asm) and shows a fatal flaw in Card Pop that makes it impossible to get the Venusaur phantom card. I'm not sure how difficult it is but can someone decompile the two European versions as well to check if this was fixed there?
Thank you!

 

[FAST6191]

I don't know if it is technically decompilation on the GBC (most things would have been assembly still) but I take your meaning. Doing it for another region might be able to take many cues from an existing work on the same system but it is still quite the endeavour. If your interest is in bug fixes between regions it would probably be easier to target that as a more general assembly hack, presumably guided by what you know of this one.
Line 316 onwards it seems had some comments

.venusaur1_or_mew2
; choose either VenusaurLv64 or MewLv15
; depending on whether the lower
; bit of d is unset or set, respectively

; since the parameters for this decision is
; based on the cumulative xoring and addition
; of the players' names, they have the same parity
; and thus, the lower bit in d will always be 1
; as a result, VenusaurLv64 is functionally unobtainable

Guess some dev hoped the random nature of things would make for a random result but fluffed the maths.
Would have to have a look when not falling asleep as I type things. Sadly for this if it is fixed to use a proper RNG/PRNG (random number generator) then the easy option of follow whatever reads the names is not going to be much of an option. Might be worth following the resulting card you get from whatever this is that triggers it back through in a more traditional tracing session as well as it will showcase how it randomises things.

 

[IngeniousDefault]

Yeah, it's really unfortunate that they messed this up and I'm not sure if they were aware of this and fixed it in the Switch release. The highest chance for it to be fixed was back with the European release.