In Battle of Immortals there a different Types of Letters / Tables.
You can get from Monster Drops.
They look like this
There are seven Types of them
The Word "Battle"
The Word "of"
The Word "the"
The Word "Immortals"
The Letter "B"
The Letter "O"
The Letter "I"
You can change all 7 of them at Atlantis [137,211]
After that you will get a Item. "Angel Heart" or "Angel Feather"
But the Problem is you need both of this Items.
So you need to collect all 7 Letters Two Times..
And if you are unlucky and get 2x Angel Hearts you need to collect them once more.
Archangel looks like this.