If I cast the Bestow Curse spell on myself, choosing the fourth curse, and then cast Life Transference, will I heal one creature for an extra 1d8?

Question

The fourth option of the Bestow Curse spell (PHB, p. 218; emphasis mine) states:

[...] While the target is cursed, your attacks and spells deal an extra 1d8 necrotic damage to the target.

The Life Transference spell (XGE, p. 160; emphasis mine) states:

[...] You sacrifice some of your health to mend another creature's injuries. You take 4d8 necrotic damage, which can't be reduced in any way, and one creature of your choice that you can see within range regains a number of hit points equal to twice the necrotic damage you take.

If I cast the Bestow Curse spell on myself, choosing the fourth curse, and then cast Life Transference, will I heal the target of Life Transference for an extra 1d8?

Answer 1

Yes, this works.

You have made the correct observations. Bestow curse causes your attacks and spells to deal an extra 1d8 necrotic damage. If you are the target of that curse, and you target yourself with a damaging spell, naturally, you take the extra 1d8 necrotic damage from the curse. Then, with life transference, because of the curse, the "necrotic damage you take" is 5d8 instead of 4d8, so that extra 1d8 gets counted toward the healing caused by life transference. The crucial point here is that the curse causes extra necrotic damage specifically. If the extra damage was any other type, it would not count toward the healing because only necrotic damage counts.

Finally, as a side note, you probably cannot use life transference to heal yourself.

Answer 2

Yes, this works - with a few caveats

First, as pointed out by KilrathSly, you will need to fail your save against Bestow Curse, in order to have the curse affect you. Note that you cannot voluntarily fail a save, even against your own spell.

Second, once you have your Bestow Curse up and running, note that it is a concentration spell. As such, the damage you take from the Life Transference has a chance of ending the Bestow Curse. Even at just 5d8, that is going to be more than 20 damage most of the time, so above a DC10 Con save.

Using a third level slot (Bestow Curse) to set up some reliable bonus healing might be justified depending on your party's class composition, but using a third level slot to try to combo and then making the save on your curse, or failing the save and then having the curse fall to lost concentration the first time you use it might not be a sound strategy.

Once past these hurdles, though, you are correct. With you as the target of your own curse, "your attacks and spells deal an extra 1d8 necrotic damage to the target". Since Life Transference says "You take 4d8 necrotic damage", it would actually do 4d8+1d8 = 5d8 necrotic damage to you. This satisfies its own condition of "the necrotic damage you take" - the extra necrotic damage from the curse has become part of the spell damage from the transference and is passed on as healing to the target.

One final caution, in your question you ask "will I heal the target of Life Transference for an extra 1d8?"

No, you will heal them for an extra of twice what you rolled for the extra 1d8 damage from the curse. You don't make a separate damage and healing roll. Rather, you make a single damage roll and the healing is twice that amount, without a roll.