Bladesinger Chain is enchanted elven chain armor +4, which can be worn also by thieves and requires 5 strength points to wear this. This item has an armor class of 1 and has the same protection modifiers as normal chain mail, but this armor gives penalties to Thieving Abilities, -20% to Pick Pockets, -15% to open locks, -10% ot Hide in Shadows/Move silently and -5% to Set/Detect Traps. Bladesinger Chain has a weight of 15 lbs, but an extremely high item value, which means it can be sold for a lot of gold. This item appears in Baldur's Gate II: Shadows of Amn. This armor is dropped by Nizidramanii'yt when you kill him in the forest clearing of Suldanessellar.
You can get it as well in The Black Pits II: Gladiators of Thay as a reward item after defeating the DROWS in Tier 1 - Battle 5.
|“||The lore of this suit is difficult to determine, either due to the exotic circumstances from which it sprang, or the wish of its previous owner to conceal its location. Secrecy would certainly be desirable, as even rumors of such a mail as this could provoke deadly interest. It is the pinnacle of elven craft, and a truly blessed item.||”|