If Karthus and Machine Evangel die simultaneously from Singularity, does the controller of Karthus create 6 tokens or 3?

Ruling: When Karthus and Machine Evangel die simultaneously, the controller creates 6 tokens total. Karthus's passive ability causes Machine Evangel's Deathknell to trigger an additional time because Karthus is still on the board when Deathknell triggers are added to the chain.

Sequence:

• During cleanup step 2a, both units have lethal damage and their Deathknell abilities trigger
• The game captures the current board state, noting that Karthus is still present
• Karthus's passive ("Your Deathknell effects trigger an additional time") applies to all Deathknell triggers being added
• Machine Evangel's Deathknell is added to the chain twice (base trigger + additional trigger from Karthus)
• During cleanup step 2b, both units are moved to the trash
• The chain resolves: first trigger creates 3 Recruit tokens, second trigger creates 3 Recruit tokens

Nuances:

• Deathknell triggers are added to the chain before units are actually moved to the trash, so Karthus's passive is active even though he's dying simultaneously
• Karthus's passive applies to his own Deathknell as well if he has one