How many endings are in Slay the Spire?

There are 3 possible ways a Slay the Spire run can end.
In your sense, counting each character individually, there would be 6 possible 'endings'.

Note: Details about this might spoil the ending for new players, so the answer is hidden behind spoiler tags.

1:

You die before beating the final boss (or bosses if you play on A20).
This counts as a loss, so you cannot unlock higher ascension levels.

2:

3: (4/5/6)