Allies in the targeted area inflict and receive a maximum of 1 damage for the rest of the turn.

This analysis was written by FlashingFire.

There's never been anything quite like Impregnable Wall in a Fire Emblem game before. The ability to nullify most damage for a turn, for up to three units no less, is incredible. It is especially incredible on Maddening mode, where even frontline fighters can crumble against two or three enemies in succession.

The use cases are varied. Need to clog up an area with enemies so you can smash them with a big Gambit next turn? Wall. Squishy mages can't get away from an approaching pursuer? Wall. Need to safely bait the Death Knight? Wall. Or my personal favorite, want to watch Edelgard uselessly burn through her entire stock of Raging Storms in one turn? That's right, wall.

Each house gets rather quick access to one battalion with this gambit. The Empire Armored Co. and Kingdom Armored Co. are both D-rank, while the flying Alliance Wyvern Co. is C-rank. All three are incredible value deals that let even a unit with zero Charm extend life-saving support. Units with Canto are especially adept in this role since they'll be good at making sure they don't leave themselves within enemy range afterward. Oh, also it can be used five times per battle. That's right, five.