Delirium Portal

[Snake Hand]

Does it show up after Mega Satan if you beat Hush first? If it's chance based then I suppose I'll have to take the portal now since I don't wanna miss it

[Joshua Kurayami]

IIRC whenever you beat hush or not, you'll always get 50% for delirium portal to spawn at mega satan.

[Cutebleeder]

Hush is the only guaranteed Del portal (upper right exit of the room). But all chapter bosses starting from Mom to ???/The Lamb have a small chance to drop a portal, and then Mega Satan is a 50/50.

Edit: Beating Hush during the run is not needed to get the portal, but you have to have beaten Hush as least once to unlock it.

[Marceloid]

Not necessarily, as others said, its a coinflip.

https://bindingofisaacrebirth.fandom.com/wiki/The_Void

Elaborating on the other spawn chances for a portal, we've got:

5% after Mom (if 10+ damage or 20+ items)
10% after Moms Heart / it Lives
15% after Isaac / Satan
20% after Blue Baby / The Lamb
50% after Mega Satan
100% in the Blue Womb after defeating Hush.

Multiple portals can appear during a run. Good luck if you coinflip it!

[Nareth Erakian]

Originally posted by Marceloid:

Not necessarily, as others said, its a coinflip.

https://bindingofisaacrebirth.fandom.com/wiki/The_Void

Elaborating on the other spawn chances for a portal, we've got:

5% after Mom (if 10+ damage or 20+ items)
10% after Moms Heart / it Lives
15% after Isaac / Satan
20% after Blue Baby / The Lamb
50% after Mega Satan
100% in the Blue Womb after defeating Hush.

Multiple portals can appear during a run. Good luck if you coinflip it! :repenny:

Also, in total, if you go a usual run with the chances occuring at Mom's Heart / It Lives, Isaac / Satan and Blue Baby / The Lamb, you have a total chance of 38,8% of getting a portal. Unlocking and defeating Mega Satan increases the chance to 69,4%.
So, around every 2 out of 5 usual runs to Chest or Dark Room can get you a Void Portal, with an extra 30% when also defeating Mega Satan.