Trying to sort Link's moves by type in order to figure out which stickers they can be boosted by is some kind of exercise in futility:
Link
Neutral A, A, A: Slash + Weapon, Slash + Weapon, Slash(/Stab if it exists?) + Weapon
Up tilt: Slash + Weapon
Forward tilt: Slash + Weapon
Down tilt: Slash + Weapon
Up smash: Slash + Weapon, x3
Forward smash: Slash + Weapon, x2
Down smash: Slash + Weapon
Neutral air: Leg
Up air: Slash(/Stab?) + Weapon
Forward air: Slash + Weapon
Back air: Leg, x2
Down air: Slash(/Stab?) + Weapon
Special: Specials: Indirect + Weapon
Up special: Specials: Direct + Slash + Weapon
Forward special: Specials: Indirect + Weapon
Down special: Specials: Indirect + Weapon + Explosive (+ Throwing?)
Throw hit: Weapon
Up throw: Slash + Weapon + Throwing
Forward throw: Leg + Throwing
Back throw: Leg + Throwing
Down throw: Arm + Throwing
The thing is, if this were any other game I'd look at this nonsense and say, "Okay, there's no way the system is this complex. The throws are all probably based only on the Throwing Attack stat, the specials are all probably based only on the Specials: Direct/Indirect, and the Weapon Attack category is probably only meant to apply to A attacks that use non-sword weapons like King Dedede's hammer and Lucas' bat."
But there are two reasons I can't say that. First, it's Sakurai. :lol I'm not writing anything off. And second, there are so, so many categories of attack types that it would seem strange to me if they were really boiled down to only one attack type per move. Take Zelda's Din's Fire, for example... Is it a Magic or a Fire Attack? Why not both? Or the beloved Knee that everybody wants to return: it has elements of Leg
and Electric Attack. Or Pikachu's forward air: that seems like Body + Spin + Electric.
Ah, well, whatever. These are just the preliminary stages anyway, nothing set in stone yet. I'll just write down as many possibilities as are known.