The Bloodkindred stack — Familial Bond achievement + Vampiric Bloodline Boon — is the canonical caster self-damage build. Here's the exact unlock sequence.
Step 1: Familial Bond (Achievement)
Start a Mage character. Reach the Forest biome, locate the Upsidedown Individual encounter. Dialogue option: Allow him to take some of your blood. Defeat the resulting Ancient Vampire / Dio combat. Achievement unlocks Bloodkin Warlock subclass + 1/2 Vampiric Bloodline progress.
Step 2: Vampiric Bloodline (Boon unlock)
Visit The Veteran NPC. With the Familial Bond achievement, the Vampiric Bloodline Boon becomes purchasable for 75 Cealts. The Boon provides +3% Lifesteal and reduces self-damaging ability costs by 50%.
Step 3: Dream Ending (Achievement)
On a NEW Mage run, repeat the Familial Bond dialogue (allow him to take blood). The Dream Ending achievement unlocks when the Vampiric Bloodline Boon is already equipped. This grants Bloodkindred status — a one-time account-wide ascendancy.
Why the stack works
Bloodkin Hex costs 1% Max HP per cast (reduced to 0.5% with the Boon). At level 25 with 200 HP, that's 1 HP per cast. Lunaeia race lifesteal recovers 15% of damage dealt to bleeding targets. Net HP delta per cast: +14 HP per cast against a Bleed-stacked target.
Boon Loadout
Vampiric Bloodline (2 slots), Force of Will (1 slot), Predation (2 slots). 135 Cealts, 5 slots. Force of Will catches the inevitable Cold Day When A Bleed Target Recovers.