Rogue offhand
 

What is an ideal offhand for a rogue? Not necessarily an item in particular, but more-so stat ratios. Can I use something other than a piercing weapon for my offhand, or is it always recommended to use two piercers?

I believe you want the best ratio you can get in the offhand. It doesn't need to be piercing.

A cheap one is the Crystalline Short Sword or CSS, which is pretty cheap.

Rogue off-hand is about ratio + stats. Damage type doesn't matter (naturally not 2H or H2H), so you can pick 1HB, 1HS or piercing. Here are some examples:

Rapier of Oriin
Crystalline Short Sword
Sebilite Croaking Dirk
Jagged Blade of Mourning
Edge of the Nightwalker

You will want a slower off-hand for targets that have damage shields, and a faster off-hand if you need more push.