The deck only mainboards 2 of each curse and 1 of some others for these reasons:
1 ofs:Curse of Echoes: literally stops control decks.Curse of exhaustion: Delay's blitzy weenie decks.
2 ofs:Curse of Death's Hold: Stunts token decks.Curse of Bloodletting: Self explaining.Curse of Thirst: Also, self explaining.Curse of misfortunes: indeed self explaining.
Now, the reason i run 2 misfortunes instead of more, 3 misfortune triggers, 1 from the first one played, 2 from the following turn when 2 are in play, or additionally 3 turns with 1 misfortune in play, 9 times out of 10 will cause death.
idealistic play:
T1: no play. most people get discouraged from seeing no T1 play in standard. thats fine.
T2: more often than not you're going to drop heartless here. if they played first and are now privy to 2 lands and one of them is blue, you're probably going to see a counter spell vs. a heartless.
T3: ideal play is of course heartless, so now there ae 2 in play, and then a bitterheart for 1 black. auto dies fetch misfortunes.
T4: misfortunes triggers. now, if you're playing contol it may be worth it to get curse of echoes. if you feel you can handle it than normally this is where i put on my stall curse, exhaustion.
thats 1 trigger of misfortunes. now we enter our turn.
lets not be greedy and assume there's no land drop this turn. 3 land still. lets also assume we don't have a bitterheart in hand which would be ideal. there is however a good chance that we have an entomber exarch. so lets use 2 mana and play it. now we have a bitterheart in hand. if we are lucky enough to have 3 black producing mana, play her.
entomber and bitterheart go to the yard and you get 1 more misfortunes.
3 curses.
T5: they have taken no damage at all thus far.
misfortune's triggers. first one, lets grab a curse of thirst. second one will grab bloodletting.
now we want to play a bitterheart here. we want to get either thirst or bloodletting. either works.
end your turn.
they die on their upkeep. they have 6 curses on them. thirst triggers. 6 damage. bloodlettings trigger. 1st resolves making 12 damage. second resolves making 24 damage. GG.
additionally i am adding a modern version of this deck. it will be significantly faster.