Iroas's last ability prevents all damage dealt to attacking creatures you control, not just combat damage.

When a God enters the battlefield, your devotion to its color (including the mana symbols in the mana cost of the God itself) will determine if a creature entered the battlefield or not for abilities that trigger whenever a creature enters the battlefield.

As a God enters the battlefield, your devotion to its color will determine whether any replacement effects that affect creatures entering the battlefield apply to that God. Because replacement effects are considered before the God is on the battlefield, the mana symbols in its mana cost won't be counted when determining this.

The type-changing ability that can make a God not be a creature functions only on the battlefield. It's always a creature card in other zones, regardless of your devotion to its color. It's always a creature spell while it's on the stack.

If a God stops being a creature, it loses the type creature and the creature type God. It continues to be a legendary enchantment.

The abilities of Gods function as long as they're on the battlefield, regardless of whether they're creatures.

Counters put on a God remain on it while it's not a creature, even if they have no effect.

If a God is attacking or blocking and it stops being a creature, it will be removed from combat. It won't rejoin combat if it resumes being a creature later during that combat.

Your devotion to two colors is the number of mana symbols among mana costs of permanents you control that are the first color, the second, or both. If an effect counts your devotion to two colors, a hybrid symbol that is both of those colors is counted just once.

If an effect causes a God to lose all abilities, its ability that causes it to stop being a creature still applies if appropriate.