Mjölnir's Strike is a game mode in Fire Emblem Heroes where the player has 7 turns to defend two Gateways located at the bottom of the map from the invading army.
Thórr, the God of War has declared war on Askr. She is armed with millions of soldiers and it is up to Alfonse, Kiran, and the Order of Heroes to defend Askr against her army. Each Strike has an enemy commander which needs to be defeated in order to emerge victorious.
Mjölnir's Strike can be separated into 4 linear cycles; Brace, Shield, Counter and Rest. However it should be noted that Rest is not always in the cycle and the next Strike will start at Brace.
Brace and Rest
During Brace and Rest, the player can set the defending team and the shield map for the Shield phase.
The player can control 4 units at once, with the Pair Up mechanic being available for all units allowing a team of 8. Similar to Aether Raids, 4 defensive structures can be placed that can be activated during the Shield phase.
The defensive team menu shows a 4 x 2 table that grants bonuses depending on the row which the unit occupies. The first row is the attack role which allows the unit to attack enemies in the top 3 rows without being targeted during enemy phase. This does not stop enemies from counter attacking when engaged during player phase. The other 3 roles are Speed, Defense and Resistance. These units gain +10 of the respected stat in the lower 5 rows. There is an option to lock the team, like other game modes. Mythical seasons also applies bonuses to the Mythic Heroes, granting either +4 HP or +2HP depending if the bonus season is Major or Minor. If a Mythic Hero is deployed they are also treated as if they had additional merges, with +10 for Major and +5 for Minor. Additionally, the effect from Legendary and Mythic heroes will not boost blessed allies in this mode.
Thórr's forces' strength is determined by the strength of the player, which is based on Tier, difficulty and the strength of the heroes on the defensive team. The strength of a Pair Up unit is determined by whichever unit is stronger in this mode.
This phase is where the player can battle the army. Similar to Arena Duels, there are 3 difficulty levels; Beginner, Intermediate and Advanced and affects the strength of the enemies as well as player scoring. The map consists of 8 rows which is separated into 2. The top 3 rows allows only the attack unit to move around, and the bottom 5 rows allows only the bonus stats units to move. Structures can be activated on the players turn to either debuff enemies or buff allies. At the end of each enemy phase, a mixture of generic and heroes come as reinforcements for the player to defeat.
If an ally falls or a Gateway is destroy, it lowers the player's score. If both of the Gateways are destroyed, then it is an automatic defeat. The Shield phase lasts for 48 hours.
This phase is the only time in Fire Emblem Heroes in which Kiran is a playable unit and Breidablik is a wieldable weapon.
The counter period comes directly after the Shield phase and the player is given 3 counter arrows. The arrows cannot be saved up for a future event and will disappear after the countering period ends. The damage dealt to the enemy commander is dependent on the player's Tier and Shield score. There is a bonus when the enemy is stronger than the player and will give a x 5 multiplier bonus to the player's offensive power. Also, there is a combo bonus that is reliant on all players' combos the previous hour. Example: 1,000+ combos = x 1.1 bonus, 2,000+ combos = x 1.2 bonus.
If Askr's forces deals more damage than Thórr's forces when the event finishes, then the victory is awarded to Askr. When the player wins, the Askr level increases by 1. If the player's forces were stronger than the enemy's forces for 10 hours, the player's Askr level increases by 2. If the player is defeated by Thórr's army, the player's Askr level is decreased by 1.
The reward given to the player is determined on their score and Askr Level. The rewards from tiers include Midgard Gems, Divine Codes (Part 2) and Dragonflowers. The Askr Levels reward is Feathers, though 10 Dragonflowers are also awarded if the Askr Level is 30 after the Counter Phase.