Designing Ys, Vol. 3: Vagullion

The single most important weapon in Ys I is the Silver Sword. It is not the strongest weapon in the game; that's the Flame Sword, which it's 18 points weaker than. But the Silver Sword is the only weapon capable of harming the final boss, so unlike the Flame Sword it is indispensable to the player's progress. The credits will never roll without it.

Most games would give the second-strongest weapon in the game to the player in the final dungeon, or shortly before entering it. Ys gives it to them less than halfway into the game.

There are two immediate reasons the player needs to explore the Mines of Esteria. The first is to acquire the third Book of Ys, and the second is to acquire the Darm Key necessary to open the way to the final three books. In addition to these, the Mines are where the game's antagonist hid the Silver Armor required for the final boss, and where the player can find the Roda Seed. This last item is what enables them to speak with the massive Roda Trees on the overworld, which will eventually let the player dig up the Silver Sword from within their roots.

While the player can enter Darm Tower as soon as they have the third book and the corresponding key, doing so locks them off from ever returning to Esteria. To ensure that the player has all of the Silver equipment before proceeding, the last boss faced before entering Darm acts as an equipment check—in other words, it's supposed to be impossible to defeat without the Silver Sword, Silver Armor, and Silver Shield. And for some, it's just impossible to defeat in general.

Conceptually, Vagullion is similar to the Yellow Devil of Rockman fame. The boss begins as a single enemy, then splits into a swarm of bats that fly across the room to attack the player. Vagullion is only vulnerable in its unified form and only for a few frames, and like Nygtilger has a form of contact damage that will harm the player if they bump into its upper body. The pattern the player finds themselves pinned into is to hang close to the swarm, teasing it into attacking Adol, before darting away as it closes in and repeating this process until Vagullion reforms.

While simple in theory, there are several wrinkles to executing this strategy. First, while Vagullion is balanced around level 17, these are the player's naked stats at that level:

HP 85
ST 42
DF 35

And these are Vagullion's stats:

HP 150
ST 75
DF 56

For comparison, these are the player's stats with the fairly-average setup of Talwar, Small Shield, and Reflex Armor:

HP 85
STR 58
DF 45

Vagullion's numbers are dramatically inflated for the purposes of the equipment check, and even with the Silver equipment the bat's output is devastating:

HP 85
ST 74
DF 67

Vagullion goes from taking off a third of the player's Hit Points with each attack to shaving off 11%, but his swarm is also designed to get in two to three hits every time it makes contact, which provides the player with very little room to learn the boss' pattern before eating a Game Over. The player takes 12% off Vagullion with each hit and can bump that up to 24% with the right positioning, so they only need five clean hits to end the battle, but getting those hits in can be difficult because of one other property—Vagullion can feint the player.

The swarm is not required to reform unless the player is sufficiently far away. Thus the player that tries to simply pull away and loop right back, expecting the converging swarm to become a vulnerable Vagullion, gets a nasty surprise when it stops reuniting and instead begins chasing a player that's walking right into its trap. The probability of Vagullion feinting is determined by how far Adol is from the boss when it starts reforming, which director Iwamasa later recalled as being an addition to Vagullion's pattern created by Hasegawa Hiroshi, the second main programmer of Ys I & II. This behavior discourages the player from puppyguarding the boss, and introduces an element of randomness to its pattern that prevents it from being the exact same fight every time.

The combination of high stats, stringent equipment requirements, semi-random attack pattern, brief phases of vulnerability, and contact damage, all make Vagullion one of the most infamous bosses in Ys. It's not the most difficult boss found in the duology, but it is the one that claimed the most casualties in terms of unfinished playthroughs. It's difficult to say if the boss was supposed to be that hard—but at least when rebalancing the game for its "definitive" overseas release, Iwamasa did not see fit to make any adjustments other than the pattern changes Hasegawa came up with, whereas at least one later Ys I boss saw its stats modified and almost all major encounters of Ys II got an overhaul.