This doesn't happen often but on occasion in Fire Emblem Heroes the AI can actually stall a battle.
I bumped into this situation during a for fun Tier 20 Arena Duel match...
Now usually this doesn't last forever since by moving your heroes around they should separate to try and fight them off but sometimes that doesn't happen or the player can't afford to do that.
This would be one of the cases.
Given how Fire Emblem Heroes AI works they will prioritize Melee moving first followed by Ranged but if the Ranged Hero has Reposition you actually can get stuck lol.
This is one of the reasons why I'm certain Intelligent Systems and the team for Fire Emblem Heroes made the AI predictable and simple as even the simplest action of stalling could make it not plausible for the player to survive.
This is also why I think player vs player in Fire Emblem Heroes is pointless since it'd be all about stalls lol.
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