As we go into Slate 3, the first coveted item slate, I think it's best we acknowledge the Donphan in the room:
Leftovers
At the end of every turn, holder restores 1/16 of its max HP.
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The item used by over 95% of the Pokémon in gen 2, but, this is not to deposit the notion that leftovers is overpowered and is a 'problem' that we need to fix. No, simply by virtue of the maxed EV system, the lowered chip of no perma-sandstorm, only one layer of spikes, and the lower power of moves overall... Even stuff like Gengar can stick around for a number of turns! This means that naturally, leftovers will slot in nicely into this environment and is a snug fit. A few things can break this mold, notably Marowak's Thick Club, and more niche things like Magnet on Zapados. To the point where the second most used item in the meta is.... No item, for Thief!
What does this mean for the slate? Well, it means that any item has to keep in mind that it has to compete with Leftovers and itemless(thief), as it can be very tempting to make an item like Choice Band or Scarf that will simply make the entire balance of the tier out of wack but will have a impact regardless. I think so far our submissions have been creative and well thought out, and I believe they'll continue to do so, so let me help bring up a 'trap' of making an item submission(as I've talked with
Rezzo about this a little bit already).
GSC items are
V I S I B L E , you can confidently determine what someone is holding by playing smartly around them, even with no item thief users, you can see the no leftovers heal and be tipped off! Why signature items were chosen for slate 3 here is because these too are visible in the sense of "oh this 'mon that isn't very strong without their signature item didn't heal from leftovers, which means they probably have their signature item...", ala Marowak. This is a defining feature of GSC and while difficult, is great for the identity of the project to try and maintain.
Making an item that is strong enough to compete with Leftovers while not being overcentralizing, talking and thinking about the greater implications of any item addition is a grand time, and, again, a challenge that I look forward to going forward with y'all!