Game King's Digimon Masters Online may have the distinction of being the only Digimon MMORPG online right now, but that doesn't make it entirely accessible. Like most games, there is a brief tutorial at the beginning of the game, but it doesn't cover all the details of the game. Chances are, most players will have to retreat to the fan wiki to learn more about the game.
This becomes more pointed when the player begins following questlines. Killing rogue Digimon for quests also sees the Digimon dropping loot, from bytes (the in-game currency) to the quest item to digieggs to actual Mercenary Digieggs, which is how the player gets new Digimon. These are only a few things that can be dropped by rogue Digimon--there are other things dropped depending on Digimon and location, such as seals.
Seals are flat with a green aura when dropped and blue in the inventory. The in-game description, when hovered over, is that these seals will help against the attacking Digimon. What it doesn't explain until the player tries to activate it is that they require a Seal Opener to activate--which requires the player to get it from the cash store, a player store, or as a very rare event item.
Once you get a seal opener, you'll want to know how many seals to use with one--they go for an average of 400 mega (400,000 bytes) through player stores, so you'll want them to go as far as you can. One seal opener is good for up to fifty seals, so you'll want fifty seals to get your money's worth. Every extra fifty seals requires an extra seal opener. Once you have a seal opener, you right-click on a stack of seals to open the dialogue box. To deactivate the seals, you will need a seal closer, which can also be obtained through cash or player stores. The seals themselves can also be bought and sold through player stores.
At this point, it's worth asking what seals are good for. Simply put, it boosts the stats of every Digimon you own instead of one at a time as Digiclones do. Depending on the seal, you can boost attack, defense, health, digi-soul (the game equivalent of mana), attack speed, block capabilities, critical hit ratios, and evasion chances. As you activate more of that seal, your seal rank goes up and your bonuses from that seal increase. Once you reach Master level at 3,000 of a single Digimon seal activated, you get the highest percentage that particular seal has to offer.
Now, are these seals worth the trouble? Well…yes, actually. Even a small percentage improvement in any of the aforementioned stats makes a world of difference in battle. It's little wonder that players will happily farm areas with Digimon that drop seals with that in mind. However, since many of these Digimon will also be linked to story and daily quests in the area, it is important to consider player etiquette when seeking to farm these seals. Pausing every once in a while to check for nearby waiting players is important, and picking a less populated channel will reduce this need. For larger areas with a greater population of the target Digimon, farming a small section leaves plenty for quest-goers. If you're doing a quest, vacating the area when you're finished is the courteous thing to do.
So seals do make a major difference to the game. Unfortunately, the game itself doesn't give much indication that these items are useful. Figuring out their use requires either trial and error or consulting a wiki or fan guide. Sadly, it's a failing of the game that players have to go to external means to learn more of their gameplay, especially when doing so improves the gaming experience.