This adds evolution methods where an evolutionary stone will only trigger when the Pokémon is a particular gender, like the Dawn Stone for Kirlia -> Gallade and Snorunt -> Froslass.
Additionally included is an evolution method where an evolutionary stone will only trigger when the Pokémon is holding a particular item; said held item will be removed during the evolution. This could be used alongside a Link Cable evolutionary "stone" to handle Pokémon that evolve by trading while holding an item.
Open config.s in a text editor.
Decide where you want the code to be inserted, and update the defition of free_space to match.
If you have expanded the number of evolutions per Pokémon beyond 5, make sure to update EVOS_PER_MON to match.
The rest of the configuration is assigning evolution method ids. For example, evolving by trade is id 0x06, and evolving by happiness is id 0x01. Naturally, they need to be unique. An unmodified FR has 15 evolution method ids, ranging from 0x01 to 0x0F, so the first new evolution method added should be 0x10 and so on.
Pick an evolution method id for evolving male Pokémon with an evolutionary stone and update EVO_ITEM_MALE with it. Alternatively, set EVO_ITEM_MALE to 0x00 if you don't want that evolution method inserted.
Pick an evolution method id for evolving female Pokémon with an evolutionary stone and update EVO_ITEM_FEMALE with it. Alternatively, set EVO_ITEM_FEMALE to 0x00 if you don't want that evolution method inserted.
Pick an evolution method id for evolving Pokémon holding a held item with an evolutionary stone and update EVO_ITEM_HELD_ITEM with it. Alternatively, set EVO_ITEM_HELD_ITEM to 0x00 if you don't want that evolution method inserted.
Copy your ROM to this folder and rename it rom.gba.
You'll need armips for the next part.
Open a terminal / command prompt and run armips evolutionary-stone.asm. This will create a modified copy of rom.gba in test.gba; rom.gba will not be modified.
The relevant keys in the ini are NumberOfEvolutionTypes, EvolutionNameX and EvolutionXParam.
For the sake of example, I will assume these were the first evolution methods you've added and they were added as 0x10, 0x11, and 0x12 (written in decimal, 16, 17, and 18). I would do:
NumberOfEvolutionTypes=18
EvolutionName16=Item w/ Held Item
Evolution16Param=item
EvolutionName17=Item w/ Male
Evolution17Param=item
EvolutionName18=Item w/ Female
Evolution18Param=itemThat will allow you to assign these evolution methods to Pokémon and their associated evolutionary stones.
Setting the held item of a Item w/ Held Item evolution will require hex editing, because the held item is stored in the two padding bytes which PGE does not support editing.
If that's enough for you to understand how to set it up, you can stop reading here. If not, read on.
You'll need to calculate gEvolutionTable + i * (8 * EVOS_PER_MON) + (8 * j) + 6, or more succinctly gEvolutionTable + 8 * (i * EVOS_PER_MON + j) + 6, where i is the species id of the Pokémon in question and j is the "evolution slot id" where 0 would be that Pokémon's first evolution slot, and 1 would be the second evolution slot, and so on. Just pull up that address in a hex editor and put the held item there.
In an unmodified FR, gEvolutionTable is located at 0x08259754, and of course EVOS_PER_MON is 5.
For an example, we'll set up Seadra's evolution into Kingdra. SPECIES_SEADRA is 0x75, and ITEM_DRAGON_SCALE is 0xC9. We're going to put this evolution in the second slot, keeping the standard Trade w/ Item evolution into Kingdra in the first. We'll also assume that gEvolutionTable and EVOS_PER_MON are still vanilla.
Set up the evolution as much as possible in PGE, then put C9 00 at 0x08259754 + 8 * (0x75 * 5 + 1) + 6 = 0x0825A9AA in a hex editor.