1. Is there any chance that Flinging mushrooms, or perhaps Big Root causes Leech Seed or any other effect? Are there other items that have special effects (such as heart scale or destiny knot causing attraction, or red shard/fire stone causing fire-type damage or burn, or grip claw causing trapping, or razor claw critical-hitting or having higher Crit-hit rate, or shed shell causing switching, or Shoal Shell having an effect, or Electrizer or Deepseatooth or Protector doing things, or Amulet coin causing behaviour similar to Pay Day)?
Sorry, no damage calcs on these. Most were Flung before the opponent's first attack, with the exception of Choice Band, which I was hoping would cause Encore, and Leftovers, which I was hoping would have a healing effect. The targets were all Raticates and Fearows.
Amulet Coin - No perceived effect
Big Mushroom - No perceived effect
Big Pearl - No perceived effect
Big Root - No perceived effect
Choice Band - No perceived effect
Destiny Knot (on opposite-gendered target) - No perceived effect
Escape Rope - No perceived effect
Fire Stone - No perceived effect
Focus Band - No perceived effect
Focus Sash - No perceived effect
Heart Scale (on opposite-gendered target) - No perceived effect
Honey - No perceived effect
Lagging Tail - No perceived effect
Leftovers - No perceived effect (used on a damaged target)
Life Orb - No perceived effect (no recoil, either)
Light Clay - No perceived effect
Metronome - No perceived effect
Nugget - No perceived effect (less damage than you'd think, too)
Pearl - No perceived effect
Razor Claw - Doesn't automatically crit (sorry, Tauros)
Red Shard - No perceived effect
Scope Lens - Doesn't automatically crit (sorry, Primeape)
Shell Bell - No perceived effect (and no HP regen after the Fling)
Star Piece - No perceived effect
Sticky Barb - No perceived effect (confirmed to not stick to an empty-handed target)
TinyMushroom - No perceived effect
This list is not exhaustive, but after trying all these items, I propose a theory: the list of Fling items obtained from the Japanese site is complete, in a sense. It appears that all items not on that original list do the same (minuscule) amount of damage and have no special added effects.
P.S. I didn't realize that using Honey in tall grass summons a random encounter, like Sweet Scent. Probably not news, but I thought I'd mention it.