Iron Wall?

This is one skill that has baffled me. Since the Colo event, I've probably been in at least 200 battles and have a mlbBernhard on my team. What exactly does Iron Wall do and how does the skill activate? I have yet to see an attack be nullified to 0? Is that what the skill is supposed to do? Or am I missing out on something xD

Iron Wall is a Battle Arena exclusive skill, this event is a Colo event.

Iron Wall completely negates the damage/effect (not completely sure on effect) of the opponent's unit.

Another question about Iron Wall...if a unit has two skills, are they both available in the Arena?

For example, I know Bajardo has Iron Wall and KNockback. Does his KB ability still activate in Arena or just Iron Wall?

Just Iron Wall.

I'm also assuming that applies for all Arena skills than? IT applies over the other skill unit has (if they have 2)

I've seen Bernhard activate iron wall in this guild event. And was quite brutal as it happened for me 3x in a row. T_T

It completely negated my attack, doing no damage. My units did not activate any skill, so I can't say anything about that. So, 3 of my units completed wasted their turns at the beginning for me when that happened.