Completion Marks question

[topolskiego]

Is it possible to acquire both Mega Satan and ???/The Lamb Completion Marks in one run? If I kill ???/The Lamb and don't enter Golden Chest and then go back to Mega Satan door will I get 2 Completion Marks or only Mega Satan one?

Ergo is it required to enter Golden Chest for completion mark?

[JellyPuff]

Yes, you can go kill The Lamb/Blue Baby and then fight Mega Satan. You don't have to enter the door to Mega Satan right away. Once it's open, it stays open.

[topolskiego]

Wow, you're fast :D

[topolskiego]

But will I get 2 marks if i return to satan?

[TheGreatSirNiko]

Yes, you will get the completion marks for both ???/The Lamb and Mega Satan if you kill them both in one run this way. The completion mark is awarded upon the death of the boss.

This also means there's no risk in the event that you kill ??? or The Lamb but die afterwards, before entering the chest. You've already earned the completion mark.