Wandering Vagrant

Tactics
The Wandering Vagrant only deals damage through the nematocysts (bioluminescent orbs) that it shoots out, which are propelled outward and then streak toward the player. By simply moving, you can avoid all damage from this boss. It doesn't use its attack often, making it a very easy boss; just keep moving and shooting if you're a ranged character, and if you're a melee character, just stand on it, using your attacks, and then move when it shoots.Wandering Vagrant

The nematocysts' targeting is similar to that of the game's seeker rockets in that they impact appoximately where the target was at the time of firing. They also do not detonate on hit, allowing players to typically move directly through them. However, on occasion they have been known to detonate immediately, possibly related to lag or a character being directly on top of one as it changes direction after being released from the boss.

Take care with allies when this boss is around. You or they may be caught by cross-fire as the blasts track their main target. Attempting to run the same direction as, but slightly behind, the main target is typically the fastest way to die.

This boss is extremely easy when using the Loader character. I find the best strategy for this boss is to stand on top of it using the "Z" attack constantly and when it fires out the nematocysts use the "X" ability to become invulnerable to them. Due to the slow rate of attack, you should be able to have it recharged once the next wave of nematocysts come out.

Variants
Blazing - This Elite version spawns on Monsoon. Its nematocysts are all an angry red color instead of red/yellow/green/blue, but do not appear to move any faster or be more numerous. They may have the Brilliant Behemoth effect, causing a larger than normal splash. It does not fire rockets like other Blazing elites do. Unlike the base variant, it also will cause damage if you touch its head. On the first level, Monsoon difficulty, without Glass or any items, it dealt 5 damage/sec to the Miner.

Overloading - This Elite version spawns on Monsoon or with Honor activated. Its body does not have the typical Tesla Coil effect like other Elites, but its blue-colored nematocysts will zap characters within their proximity. Without movement speed boosts, a character can dodge the nematocyst detonation, but will be hit by the electric discharge. This can change a first-level, early-triggered Vagrant from mostly harmless to considerably deadly.

Young Vagrant  - A smaller version (only about 2x taller than player characters) that only spawns on Risk of Rain (Level). It acts exactly like the larger version and has an Elite-style health bar instead of displaying a boss bar overhead. Many may spawn at once, and typically more spawn by the time they are killed.