Bovis

Zwei is one of the twelve Dark Warlords.

In Fire Emblem: Seisen no Keifu, little is said about the Dark Warlords, but they are all fought in the Final Chapter near Barhara and eventually defeated, including Zwei.

In Fire Emblem: Thracia 776, Zwei is fought in the Final Chapter. The character that becomes Zwei is Galzus if Galzus is either dead or not recruited.

Like all the Warlords his name is a german number, in this case it is two.

Seisen no Keifu
With the skills Pursuit, Critical, and Charge, it's best to take out Zwei at a range, or with a character with Awareness. All the Dark Warlords are dangerous, and Zwei is no exception, so try to divide the Dark Warlords up so you don't have to spread yourself too thin, and someone like your Holsety User can be freed up to take Zwei done with little effort.

Boss Stats
|Hero |None |30 |80 |25 |16 |25 |25 |4 |20 |16 |6 |0 |3000 |Pursuit Critical Charge |Sword - A |Silver Blade

Thracia 776
Be very careful when fighting Zwei. He has both Moonlight Sword and the deadly Shooting Star Sword, so you should try to rearrange your units till you have a strong unit that can fight at a range near Zwei's position. Failing that, you can use a Sleep Staff on him and defeat him anyway you like.

Boss Stats
|Hero |20 |54 |20 |9 |20 |20 |17 |14 |18 |7 |0 |5 |3 |Moonlight Sword Shooting Star Sword |Sword - A Axe - A |Master Sword Master Axe Flame Sword Vulnerary x2

Boss Stats
|Bow Knight |15 |54 |25 |1 |28 |26 |16 |20 |11 |8 |Early Initiative |? |Brave Bow