Lost Kin

"Shattered corpse, reanimated by infected parasites. The shape of this creature... I have seen something like it before. More than once, perhaps. It looks a little like the bugs of Hallownest, but not quite the same. Where did these empty little wanderers come from?"

The Lost Kin is a hidden boss in Hollow Knight. It is the Dream variant of the Broken Vessel, faster and tougher than its physical counterpart.

Behaviour and Tactics
The Lost Kin shares the same basic attacks as the Broken Vessel but at a much faster pace. Notable changes are:
 * Aerial Slash: Broken Vessel will fall much faster after finishing the slash.
 * Leap: Broken Vessel will rise and fall much faster.
 * Cascade: The Lost Kin no longer uses this attack.
 * Slam: When the Lost Kin hits the ground, six blobs of infection now fly out as opposed to four.
 * Balloon: This attack now happens at much quicker intervals (2-3 seconds). There is a maximum of 6 balloons that can be alive at once and this attack will only occur after the Lost Kin has reached 1150 hp.

Dealing with the Infected Balloons can be the trickiest part of the fight as they can prevent healing at the rate that they spawn. Unnecessary damage can also be taken when trying to dodge the Lost Kin's attacks and colliding with them.

Defender's Crest offers the best barrier around the Knight which can be used to heal. Other area of effect charms like Thorns of Agony and Spore Shroom can also be very useful to take out groups of Infected Balloons. Baldur Shell, when combined with Thorns of Agony, is also very helpful in this role. Shape of Unn combined with Quick Focus is useful for dodging the Infected Balloons. This approach can be more useful in the setting of the Pantheons, where the Lost Kin isn't fought in isolation, as it is generally more useful against other bosses than Defender's Crest.

As with the Broken Vessel, it is recommended to stay low to the ground as Lost Kin jumps around a lot. The only reason that would warrant jumping would be to avoid the slash attack.

Like the Broken Vessel, Lost Kin takes knockback from attacks. As such, Vengeful Spirit/Shade Soul is useful against them as well, especially when combined with Shaman Stone. Desolate Dive/Descending Dark is just an all-around good spell to use in this fight thanks to its invincibility frames and range to clear Infected Balloons too.

The Lost Kin also staggers very easily meaning that using Quick Slash can easily knock them down and allow for a moment to heal.

If the Shade Cloak has been acquired, it is technically possible to dash through Lost Kin's Slash attack. However, this is inconsistent as Lost Kin is extremely fast and can sometimes perform the Slash attack before the Knight recharges their Shade Cloak or if dash is used too early or too late, resulting in unnecessary damage. It is better to down strike Lost Kin during the Slash attack instead, as this allows for more consistent damage.

Location
The Broken Vessel to be Dream Nailed can be found where it was first defeated, near the far left corner of the Ancient Basin, guarding the Monarch Wings upgrade.

Trivia

 * Lost Kin, unlike other Dream Boss variants and Warrior Dreams, does not speak to the Knight upon defeat, but rather just gives the option to "Accept", where they will bow down at the Knight once before disappearing and giving Essence.
 * The arena where the Lost Kin is fought in Godhome is the same as the Broken Vessel's. The difference, however, is that the Infection's presence is replaced with vines and roots.

References

Fratello Perduto Zaginiony Krewniak