Sealed Weapons are an item obtained from Treasure Chests that appears in Hyrule Warriors. When obtained from a Treasure Chest, they unlock either new weapon types (ones obtained in either Legends or Free Mode) or higher level weapons (those found in Adventure Mode) on the results screen after completing a scenario. Weapons obtained from Sealed Weapons are zero star weapons with empty skill slots and basic attack power (Attack Power is based on the weapon's level and number of stars) for a weapon of its specific level (from default Level 1 to Level 3). Once a Sealed Weapon obtained from a scenario, a Weapon Bag containing a random weapon will appear in the chest on subsequent playthroughs of that scenario.
Sealed Weapons are often used to obtain a moveset's higher level weapon. All movesets, save for the Master Sword have different Levels for each moveset.
Level 1 weapons are a moveset's default level and are the first level the player receives upon unlocking a moveset and/or character. Level 1 weapons generally have the lowest base attack power and are generally less powerful that higher level weapons, even with a Five-star rating.
Level 2 weapons are mid-tier weapons and usually the second level weapon a player obtains for a given moveset. In most cases, Level 2 weapons are obtained by acquiring its corresponding Sealed Weapon in either Legends Mode or Adventure Mode. They are generally stronger than Level 1 weapons, but weaker than higher levels.
In Hyrule Warriors, Level 3 weapons a moveset's final weapon level and are the stronger than either Level 1 or 2 weapons. They have high base attack and often possess a large number of skill slots. Save for certain DLC weapons, Level 3 weapons are generally unlocked via obtaining Sealed Weapons in Adventure Mode.
Exclusive to Hyrule Warriors Legends, Level 4 weapons are basically stronger plus versions of Level 3 weapons. Level 4 weapons are unlocked exclusively by obtaining their corresponding Sealed Weapon in Adventure Mode (Sealed Level 4 DLC weapons are found on DLC Adventure maps).
As part of the Link's Awakening DLC, Level 4+ or Multi-Element Weapons are special Level 4 weapons that have an extra elemental attribute in addition to their standard attribute. Only one attribute will be active at a time. The active attribute is determined by whichever will be more beneficial based on the current enemy or situation. They can be unlocked on the Koholint Island DLC Adventure Mode map.
8-Bit Weapons are a DLC weapon level exclusive to Hyrule Warriors. Excluding DLC character movesets, each playable character can obtain 8-Bit weapons for any of their non-DLC movesets. 8-Bit Weapons are weapons based on items and objects from early Zelda titles such as The Legend of Zelda. Some of the items/objects they are based on may not match its weapon moveset, such as 8-Bit Arrows, Boomerangs, and Magic Keys being used as swords. Due to being 3-dimensional weapons based on 8-Bit 2-dimesional items/objects, 8-Bit weapons generally appear blocky and/or look humorously out of place in comparison to wielder's more detailed character model.
In Adventure Mode, 8-Bit Sealed Weapons are represented by a star symbol in a Scenario's Victory Rewards section and are obtained exclusively on DLC Adventure Maps. 8-Bit weapons are generally equal to Level 3 weapons in terms of base attack strength and number skill slots. These Level replaced by the stronger Level 4 weapons in Hyrule Warriors Legends.
Sealed Weapons found in Legends and Free Mode (which is basically a Free Play version of Legends Mode that allows one to play with any playable character that has been unlocked) are new weapons that serve as alternative weapon-based movesets that differ from the characters default weapon movesets. These include weapons like Link's Magic Rod, Impa's Naginata, or Lana's Spear. These weapons are usually default Level 1 weapons such as Link's Fire Rod which is his default Level 1 Magic Rod, though some Level 2 weapons can also be obtained such as Link's Level 2 Hylian Sword and Impa's Level 2 Giant Blade. In Hyrule Warriors Legends, Tetra and King Daphnes can unlock their Level 2 weapons in Legends Mode as well.
Sealed Weapons found in Adventure Mode require the player to receive a Gold A rank in specific scenario in order for the Treasure Chests containing them to appear after achieving victory (by completing the main objective of said scenario) in a scenario. In addition to those found on the main Adventure Map, various DLC Adventure Maps feature Sealed Weapons that unlock 8-Bit versions (which are based on various items from the 8-bit Zelda titles) of various Weapons.