You need to have two 1/1 creatures in play for this combo to work.
With all cards in play, deal combat damage to the opponent with Hapatra.
With Hapatra's ability, put a -1/-1 counter on a 1/1 creature, destroying it.
Bastion of Remembrance's ability will trigger, the opponent will lose 1 life.
Hapatra's ability will trigger, put a 1/1 token into play
Blowfly Infestation's ability will trigger, put a -1/-1 counter on the second 1/1 creature.
Abilities will trigger again, this time put Blowfly Infestation's counter on a 1/1 token
Repeat process for infinite damage