Board Thread:Question and Answer/@comment-29547733-20161124004922/@comment-25151790-20161124022158

You can reach ATK +100% from unit bonuses (5 same element GURs: ATK +10% and +25%), max friendship (ATK/DEF +5%) and three max leveled elemental buildings (3x ATK/DEF +20%). The rest can be obtained from cards with Autoskill (ATK) or Autoskill (DEF), such as Celestial Oracle (ATK +100%). Optionally, you can also use an Upgrade Potion (ATK/DEF +20%) or Upgrade Potion+ (ATK/DEF +100%) to further boost your stats.

The current highest possible ATK bonus is probably: Total: +745%
 * Krazy Kitty Kat (+150%) + 4x Celestial Oracle or Demiurge (+100%) = +550%
 * Unit bonuses: Godlike Rare Force (+25%) + Red Passion I (+5%) = +30%
 * Max friendship = +5%
 * All max level elemental buildings = +60%
 * Upgrade Potion+ = +100%