You draw a card no matter how Terrarion winds up in a graveyard from the battlefield.

You get the mana before you draw the card.

You can get either two mana of the same color or one mana each of different colors.

You must choose the colors of mana Terrarion produces before its last ability has you draw a card.

Terrarion’s last ability triggers no matter how it’s put into a graveyard from the battlefield.