Upgrade Core (Highest)

Introduction
A comprehensive list of cores can be found here. Upgrade cores are mainly used for upgrading items level(+1, +2, etc), more info can be fond here. Other types of upgrade cores are as follows:
 * Upgrade Core (Low)
 * Upgrade Core (Medium)
 * Upgrade Core (High)
 * Upgrade Core (Highest)

Obtained

 * Field: Lakeside, Mutant Forest, Pontus Ferrum, Porta Inferno
 * Dungeon: Forgotten Temple (B1F), Forgotten Temple (B2F), Forbidden Island, Altar of Siena (B1F), Altar of Siena (B2F), Illusion Castle Underworld, Illusion Castle Radiant Hall, Maquinas Outpost, Chaos Arena Lv3~6
 * DX Dungeon: All DX Dungeons