<t>>>Items inside the Lemming Castle (not in any particular order, because it's a teleporter maze):<br/> - Magical Gem<br/> - OmniGuard<br/> - Large Magazine<br/> - Fine Medkit<br/> - Fairy Wings<br/> - Fortune Disc<br/> - Revive All<br/> - Dog Tag<br/> - Ancient Metal<br/> - Elementite Plating<br/>...

Those are IAP lottery summons (3% chance to get one of these five). No, they can't be found elsewhere in the game.

#211 is Maidame Curie. As in, the infinity HP one from Unison Crisis (renamed Gazillion Challenge, basically). You can find that at Forgotten Sanctuary.

Also, fun fact - given that Can's Support Effect name is "The Name of Rust?", they are probably not made out of tin

<r>[tabs]<br/> [tab title = "Empty tab"]<br/> [/tab]<br/> [tab title = "Fallen Izayoi"]<br/> <LEGACYFILE legacyfile="26566">[legacyfile=26566]</LEGACYFILE><br/> [/tab]<br/> [tab title = "Holy Nemesis"]<br/> <LEGACYFILE legacyfile="26567">[legacyfile=26567]</LEGACYFILE><br/> [/tab]<br/> [/tabs]<br/> ...

<r>[tabs]<br/> [tab title = "Empty tab to hide images"]<br/> [/tab]<br/> [tab title = "Aries Hot Spring"]<br/> <LEGACYFILE legacyfile="26561">[legacyfile=26561]</LEGACYFILE><br/> [/tab]<br/> [tab title = "Safira"]<br/> <LEGACYFILE legacyfile="26562">[legacyfile=26562]</LEGACYFILE><br/> [/tab]<br/> [...

<t>Half-transparent turtles: If talked to with the right character in lead, turtles give +5 to that character's skill proficiency (the character's ability to interact with certain things in overworld when they're in lead). Character depends on image: portal image means Darius, sword - Erica, flower ...

<t>1) They give weapons (~180 dmg) in exchange for collectible stones<br/> <br/> 2)<br/> Chain (3 Tray) - Gold Zone, 2nd screen, look left<br/> Sword (4 Bright) - Metal Zone, 1st screen, go left from entrance<br/> Tray (4 Dark) - Mount Atochi, 1st screen from North, go up from entrance<br/> Dolly (3...

There is, and it's called Undine Ring.

It's from beating Secret Battle Arena's highest tier battle 2 times, I think.
EDIT: Yes, definitely from that:

<r>Well, for me the only requirement to equip more than 1 Disco Rings is for the character in question to be in one of these slots:<br/> <LEGACYFILE legacyfile="23596">[legacyfile=23596]</LEGACYFILE><br/> That said, the whole thing seems to be a glitch anyway, so I can't really guarantee that it wil...