Can a hidden Teemo be played as a reaction after Kog'Maw's Deathknull triggers and resolves at a battleground where there are currently no units (since hidden cards get sent to trash at end of combat when there are no units)?

Ruling: Yes, you can probably play the hidden Teemo as a reaction after the Deathknull triggers and resolves.

Nuances:

• This part of the rules is considered broken and disagreed upon by the community
• The answer is not definitive ("probably")