RainingChain Posted September 8, 2023 Share Posted September 8, 2023 (edited) Here's what I've discovered about Mystery Gifts in Pokemon Stadium 2. Similarities with GameBoy Color Infra-Red Mystery Gifts The logic is the mostly the same between Pokemon Stadium 2 and Mystery Gift between GameBoy Color using infra-red system. The game chooses a random item and decoration separately. The game first tries to give the decoration but you already have that decoration, you will get the item instead. Choosing a specific item or decoration gift to send occurs in two stages. First, the game selects a set from which the gift will come. Then, it uses a part of the player's Trainer ID number to determine which gift from that set to send. (Below, bit 0 refers to the least significant bit of the Trainer ID and bit 15 refers to the most significant bit. Given the Trainer ID 32768, which translates to 1000000000000000 in binary, bit 15 is 1 and bit 0 is 0.) The logic for determining the item given is the same as the logic for Mystery Gift between GameBoy Color using infra-red system. See https://bulbapedia.bulbagarden.net/wiki/Mystery_Gift for more info. Decoration Logic The logic for determining decoration is different however. Random number. Range . Gift set . Overall rate 1st 36-255 Common 223/256 0-35 N/A (pick a 2nd number) 2nd 72-255 Uncommon 25/256 0-71 N/A (pick a 3rd number) 3rd 72-255 Rare 7/256 0-71 N/A (pick a 4th number) 4th 154-255 Very Rare 1/256 77-153 Tentacool Doll 0/256 0-76 Tentacool Doll or Pikachu Bed 0/256 Common, Uncommon, Rare and Very Rare follows a similar logic as GameBoy Color Infra-Red Mystery Gifts (using Trainer ID). The exact bit used for each item and decoration is slightly different. Check https://bulbapedia.bulbagarden.net/wiki/Mystery_Gift for the detailed list. Upon reaching the 4th roll with 0-76, Tentacool Doll is given if Round 2 has not been unlocked and Pikachu Bed is given if Round 2 has been unlocked. No code exists to return Unown Doll (internal decoration ID 35). Why Tentacool Doll and Pikachu Bed are unobtainable You may have noticed that Overall rate for Tentacool Doll and Pikachu Bed is 0/256. Here's why: To obtain Tentacool Doll, the game must roll 0-35, 0-71, 0-71, 0-153 (assuming Round 2 hasn't been unlocked). To obtain Pikachu Bed, the game must roll 0-35, 0-71, 0-71, 0-76 (assuming Round 2 has been unlocked). Those sequences of numbers are not possible. The game uses a 32-bit linear congruential generator: result = (seed * 0x19660D) + 0x3C6EF35F; Mystery Gift logic only uses the last 8 bits of the generated random number. The last 8 bits of the generator follows a cyclic pattern: 0,95,50,233,52,3,134,45,168,231,26,177,92,11,238,117,80,111,2,121,132,19,86,189,248,247,234,65,172,27,190,5,160,127,210,9,212,35,38,77,72,7,186,209,252,43,142,149,240,143,162,153,36,51,246,221,152,23,138,97,76,59,94,37,64,159,114,41,116,67,198,109,232,39,90,241,156,75,46,181,144,175,66,185,196,83,150,253,56,55,42,129,236,91,254,69,224,191,18,73,20,99,102,141,136,71,250,17,60,107,206,213,48,207,226,217,100,115,54,29,216,87,202,161,140,123,158,101,128,223,178,105,180,131,6,173,40,103,154,49,220,139,110,245,208,239,130,249,4,147,214,61,120,119,106,193,44,155,62,133,32,255,82,137,84,163,166,205,200,135,58,81,124,171,14,21,112,15,34,25,164,179,118,93,24,151,10,225,204,187,222,165,192,31,242,169,244,195,70,237,104,167,218,113,28,203,174,53,16,47,194,57,68,211,22,125,184,183,170,1,108,219,126,197,96,63,146,201,148,227,230,13,8,199,122,145,188,235,78,85,176,79,98,89,228,243,182,157,88,215,74,33,12,251,30,229,0 The first random number is selected randomly in that list, then at every new roll, the next random number is the next one in the list. The issue is that there are no 4 consecutive numbers that are 0-35, 0-71, 0-71, 0-153 respectively. This means Tentacool Doll (and Pikachu Bed) can't be obtained. The sequence to obtain a Very Rare decoration (0-35, 0-71, 0-71, 154-255) appears once (15,34,25,164). In short, none of the Pokemon Stadium 2 exclusive decorations are actually obtainable. Special thanks to Lincoln for providing the initial disassembly of Mystery Gift functions of Pokemon Stadium 2. https://github.com/Lincoln-LM/stad2 Edited September 10, 2023 by RainingChain 2 Link to comment Share on other sites More sharing options...
RainingChain Posted September 8, 2023 Author Share Posted September 8, 2023 (edited) By using hacks, it is possible to receive Pikachu Bed, Unown Doll, and Tentacool Doll. In Pokemon Stadium 2 USA 1.0, place a breakpoint at command 0x801454F8 and alter the register V0 to 0x22 for Pikachu Bed, 0x23 for Unown Doll, or 0x24 for Tentacool Doll. Note that the Unown Doll is displayed as "DECORATION". Edited September 9, 2023 by RainingChain 2 Link to comment Share on other sites More sharing options...
SnorlaxMonster Posted September 10, 2023 Share Posted September 10, 2023 From the sounds of it, this research was all conducted on English Pokémon Stadium 2. Is it feasible that it could have been possible to obtain the exclusive decorations on Japanese Pokémon Stadium GS? (e.g. If in the localization process, they tweaked the probabilities of Mystery Gift items, but inadvertently made them impossible to obtain.) Link to comment Share on other sites More sharing options...
RainingChain Posted September 10, 2023 Author Share Posted September 10, 2023 (edited) On 9/10/2023 at 7:52 AM, SnorlaxMonster said: From the sounds of it, this research was all conducted on English Pokémon Stadium 2. Is it feasible that it could have been possible to obtain the exclusive decorations on Japanese Pokémon Stadium GS? (e.g. If in the localization process, they tweaked the probabilities of Mystery Gift items, but inadvertently made them impossible to obtain.) I just tested Mystery Gifts on Japanese version. The RNG function and the 4 consecutives check (< 36, < 72, < 72 < 77) are the same. I confirm that the Tentacool Doll and Pikachu Bed decorations can't be obtained on Japanese Pokémon Stadium either. Edited September 10, 2023 by RainingChain 2 Link to comment Share on other sites More sharing options...
suloku Posted September 12, 2023 Share Posted September 12, 2023 Really interesting info, I came here referenced via this document (leaving it here for other people, it is an easy to digest info about all gen 2 mistery gift mechanics) https://bluemoonfalls.com/pages/general/mystery-gift Pretty happy to see this finally understood, that explains those 3 afternoons I spent years ago on emulator setup, advancing the clock (years even) without getting any new decoration from stadium. Link to comment Share on other sites More sharing options...
SadayOJ Posted September 20, 2023 Share Posted September 20, 2023 Not sure if this would work or not, but I remember hearing N64's keep bits of data stored in the RAM when a game is removed while running (I want to say Rare was going to use this in Banjo & Kazooie for bonus content) is it possible to use this to put in an RNG value that would generate the string of RNG necessary? (I believe this is similarly used in a Paper Mario speedrun to manipulate the RAM values.) Link to comment Share on other sites More sharing options...
poptartFighter Posted October 5, 2023 Share Posted October 5, 2023 I'm not really sure if this is entirely appropriate for the topic, but would it be possible to create a n64 gameshark code that would modify the mystery gift sent? I.E force it to give you a certain decoration). I guess the question would depend if the RNG takes place in an addressable space for the Gameshark. Link to comment Share on other sites More sharing options...
RainingChain Posted November 24, 2023 Author Share Posted November 24, 2023 Note: On PAL Stadium 2, the code is also the same as the US and JP versions. Breakpoint on PAL: 0x80145524 Link to comment Share on other sites More sharing options...
Mark_Eire Posted 13 hours ago Share Posted 13 hours ago On 10/5/2023 at 6:35 PM, poptartFighter said: I'm not really sure if this is entirely appropriate for the topic, but would it be possible to create a n64 gameshark code that would modify the mystery gift sent? I.E force it to give you a certain decoration). I guess the question would depend if the RNG takes place in an addressable space for the Gameshark. Just spent a while trying to figure this out, but I'm afraid I'm out of my depth! Hopefully someone more knowledgeable can generate some Gameshark codes (it would be very cool to see!), or confirm if it is just not possible. @RainingChain In my attempt to make a gameshark code for PAL Stadium 2, I seemed to find the breakpoint was different. PAL Breakpoint: 0x80145658 Not sure if this different value is of any particular note. I could be making a mistake, but I began using 0x80145524 and couldn't get anything to work. Swapped over to NTSC to confirm I could change the gift, then found this value worked for PAL after some experimenting. Link to comment Share on other sites More sharing options...
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