If both players don't play a Tamer for this card's ＜On Play＞＜When Digivolving＞ effect, do I still perform ＜De Digivolve 1＞?

Yes, you do. You perform the part of the effect after "then" regardless of whether or not a Tamer was played.

Eosmon rulings (BT17-075)

2 official rulings from Bandai, last ruled Sep 6, 2024. Straight answers to how this card actually resolves.

Effect: [On Play] [When Digivolving] Your opponent may play 1 Tamer card from their hand without paying the cost. If they don't, you may play 1 white Tamer card with a play cost of 4 or less from your hand without paying the cost. Then, De-Digivolve 1 1 of your opponent's Digimon for every 2 Tamers.
Inherited effect: [Opponent's Turn] [Once Per Turn] When an opponent's Digimon attacks, you may switch the attack target to 1 of your [Eosmon].

Official Q&A

Can I also use this card's inherited effect to switch the attack target to an unsuspended [Eosmon]?
Yes, you can.
Ruled Sep 6, 2024
If both players don't play a Tamer for this card's ＜On Play＞＜When Digivolving＞ effect, do I still perform ＜De Digivolve 1＞?
Yes, you do. You perform the part of the effect after "then" regardless of whether or not a Tamer was played.
Ruled Sep 6, 2024

Got a line that uses Eosmon? Map it in the builder and share it with a link.

Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.

Eosmon rulings (BT17-075)

2 official rulings from Bandai, last ruled Sep 6, 2024. Straight answers to how this card actually resolves.

Effect: [On Play] [When Digivolving] Your opponent may play 1 Tamer card from their hand without paying the cost. If they don't, you may play 1 white Tamer card with a play cost of 4 or less from your hand without paying the cost. Then, De-Digivolve 1 1 of your opponent's Digimon for every 2 Tamers.
Inherited effect: [Opponent's Turn] [Once Per Turn] When an opponent's Digimon attacks, you may switch the attack target to 1 of your [Eosmon].

Official Q&A

Can I also use this card's inherited effect to switch the attack target to an unsuspended [Eosmon]?
Yes, you can.
Ruled Sep 6, 2024
If both players don't play a Tamer for this card's ＜On Play＞＜When Digivolving＞ effect, do I still perform ＜De Digivolve 1＞?
Yes, you do. You perform the part of the effect after "then" regardless of whether or not a Tamer was played.
Ruled Sep 6, 2024

Got a line that uses Eosmon? Map it in the builder and share it with a link.