

Q1: Can I process the part of the effect after "then" in this card's Start of Your Main Phase effect without meeting the "by" condition?
No, you can't. You can only process the part of the effect after "then" in this card's Start of Your Main Phase effect if you return this card to the bottom of the deck.
Q2: At the start of my main phase, this card's Start of Your Main Phase effect plays a card. Can I then activate the Start of Your Main Phase effect on the played card?
No, you can't activate it.
Q3: Can I process the part of the effect after "then" in this card's Your Turn effect without meeting the "by" condition?
No, you can't. If you don't suspend this card, you can't process the part after "then" in its Your Turn effect.
Owen Dreadnought BT24-082 R LIBERATOR [Start of Your Main Phase] By returning this Tamer to the bottom of the deck, you may play 1 [Owen Dreadnought] from your hand without paying the cost. Then, if you don't have a Digimon, you may play 1 [Elizamon] from your trash without paying the cost. [Your Turn] When any of your Digimon digivolve into a [Reptile] or [Dragonkin] trait Digimon, by suspending this Tamer, that Digimon gets +3000 DP for the turn. Then, it may attack. --- [Security] Play this card without paying the cost.
Owen Dreadnought BT24-082 R LIBERATOR [Start of Your Main Phase] By returning this Tamer to the bottom of the deck, you may play 1 [Owen Dreadnought] from your hand without paying the cost. Then, if you don't have a Digimon, you may play 1 [Elizamon] from your trash without paying the cost. [Your Turn] When any of your Digimon digivolve into a [Reptile] or [Dragonkin] trait Digimon, by suspending this Tamer, that Digimon gets +3000 DP for the turn. Then, it may attack. --- [Security] Play this card without paying the cost.
Owen Dreadnought BT24-082 R LIBERATOR [Start of Your Main Phase] By returning this Tamer to the bottom of the deck, you may play 1 [Owen Dreadnought] from your hand without paying the cost. Then, if you don't have a Digimon, you may play 1 [Elizamon] from your trash without paying the cost. [Your Turn] When any of your Digimon digivolve into a [Reptile] or [Dragonkin] Digimon, by suspending this Tamer, that Digimon gets +3000 DP for the turn. Then, it may attack. --- [Security] Play this card without paying the cost.
オーウェン• ドレッドノート BT24-082 R リベレイター 【自分のメインフェイズ開始時】このテイマーをデッキの下に戻すことで、自分の手札から、「オーウェン• ドレッドノート」1枚をコストを支払わずに登場できる。その後、自分のデジモンがいないなら、自分のトラッシュから、「エリザモン」1枚をコストを支払わずに登場できる。 【自分のターン】自分のデジモンが特徴に「爬虫類型」/「竜人型」を持つデジモンに進化したとき、このテイマーをレストさせることで、ターン終了まで、そのデジモンをDP+3000。その後、そのデジモンでアタックできる。 --- 【セキュリティ】このカードをコストを支払わずに登場させる。