So that's how you swap stats around. The meat of this is the actual values. Once you get the stat(s) you want, you'll be wanting to make the numbers bigger. This is where riding Runewake's Wild RNG Ride really comes into play, and why everyone suffers through the game picking selected stats at random:
~*~* Multipliers *~*~
How many stats you pick directly influences the end value of what's transferred. Selecting 1 stat will give you 80% of it on transfer, selecting 2 will give you a straight transfer of 100% of the value as-is, and selecting 3 or more will boost it to 110% of its original value.
In order to increase a value (and eventually overstat) you will need to select 3+ attributes per transfer. What's an overstat? You'll see something like 300/350 on a piece of gear. Normally 350 would be the max of that particular stat roll in the game. If the value is 350/350, it
turns purple to let you know it's maxed out. Overstat is to
go beyond and make it something higher, maybe
390/350 like you're some kind of final form boss character. (The actual highest you can go is 121% of the max, this is just an example.)
Equipment type and rarity also determines how you can transfer. Equipment types have to match; you can swap stats on a 2H Sword and a 2H Hammer,
[EDIT: any two 2H or 1H weapons can have stats swapped between them as long as the hand designation matches; I dunno why my brain decided to divide by weapon class when that's a different topic. Thanks to Luatan.]. Swapping between 2 Necklaces works, but you can't swap between a Ring and an Earring. As for rarity, the Giving item must be of
equal or lower rarity to the Receiving item. Your fancy
purple cape can absorb a
blue item just fine, but it
can't absorb an
orange one. (White doesn't have any stats but it's still a valid rarity so I'm including it.)
To my knowledge, all current stat transfers that consist of 3 or more selections all result in a 110% increase. It's possible that, somewhere in the game, more than that yields higher returns but I haven't seen it yet and I don't know anyone that has. That said, there aren't many madlads other than Hater that would try to transfer 6 stats off something for kicks.