Heavily plated. Keep your footing when struck by enemies, but stopping may be a problem!
The Mail of Momentum is a black Armor with red horns that costs 6000 gold. It considerably reduces knock back when struck by enemies but also lowers Shovel Knight's traction meaning he doesn't stop immediately.
This Armor means Shovel Knight is less likely to get knocked into pits or onto spikes by knockback but the reduced traction makes one more likely to fall into pits or onto spikes in the first place.