How to make item combining on floor

YEESSS, I need this for my mod. I'm making an anime mod which includes Fullmetal Alchemist. When you place a transmutation circle on the ground and two objects, they will combine into something else. But it has to be certain objects. How would we go about doing this?

Ik this is doable with commands. I just don't know how. But I think there's a tutorial in YouTube just search Minecraft floor crafting tutorial

This is an example of floor crafting: (example of 4 items one output - should be a tick function)

execute as @e[type=minecraft:item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b},OnGround:1b}] at @s run execute as @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b},OnGround:1b},distance=..1] at @s run execute as @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b},OnGround:1b},distance=..1] at @s run execute as @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b},OnGround:1b},distance=..1] at @s run function name_space:function

The next function should have: (This should be the output function from the previous command/function)

##-------------------------------------------------------------------------------------------------
## summon items - you can add name, attributes, etc.
##-------------------------------------------------------------------------------------------------

summon item ~ ~ ~ {Item:{id:"minecraft:iron_sword",Count:1b}}

##-------------------------------------------------------------------------------------------------
## kill items
##-------------------------------------------------------------------------------------------------

kill @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b}}]
kill @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b}}]
kill @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b}}]
kill @e[type=item,nbt={Item:{id:"minecraft:an_item/block_here",Count:1b}}]

##-------------------------------------------------------------------------------------------------
##effects - optional
##-------------------------------------------------------------------------------------------------

particle minecraft:dragon_breath ~ ~ ~ 0.4 0.5 0.4 0.01 10 normal

##-------------------------------------------------------------------------------------------------
##sounds - optional
##-------------------------------------------------------------------------------------------------

execute as @a[distance=..5] at @s run playsound minecraft:block.bamboo.hit master @s ~ ~ ~ 1 0 1

You can modify it as much as you like

Well, I was hoping not to have to do it with commands, but if that's the only way then it works. How would I do it an Mcreator tho? For my transmutation circle, I made a custom block that has almost no length so that it looks like it's just a circle on the ground. But anyway, how would I make the transmutation block sense the blocks that are on top of it? And would I have to get the execute command block in order to execute that command?

That is the only way I know (not the only way it is done). The tick function does not depend on blocks or location. These functions go in a datapack, Use a test world (with your mod), create a datapack which uses your modded items/blocks, once you are happy with the results, inject/merge the datapack into your mod. You can use any item/block/armor. Maybe you could do it with procedures, but I have never tried.

A datapack is per world, but a mod with the custom datapack in it works in every world.

Let's say you want to spawn a Boss entity: the tick function can include vanilla and modded items/blocks, and the output is to summon your custom modded entity or many entities or maybe an entity in a custom structure ... anything goes.

I did something very similar here with the minecarts - it has custom minecarts and minecarts going up with custom rails.

https://mcreator.net/modification/78806/custom-3d-elytraarmor