Rulings
Q1: This card's Start of Your Main Phase effect and BT18-004 Puroromon's inherited effect triggered simultaneously when I had no face-up security cards. At such times, can I use BT18-004 Puroromon's effect to place a card from my hand face up as my bottom security card, then use this card's effect to gain 1 memory?
Yes, you can.
Q2: What happens to cards placed face up in the security stack by effects?
They become face-up security cards that remain revealed. Other than rules that specify face-up security cards, the rules apply in the same manner as standard security cards.
Q3: What happens upon a security check for a security card that is placed face-up?
The check is performed with the card left revealed. Other than rules for cards left revealed, the rules apply in the same manner as standard security checks.
Q4: Does a card's Security effect trigger upon a security check with that card placed face-up?
Yes, it triggers.
Q5: What happens if I shuffle a security stack that includes security cards placed face-up?
Any face-up cards are placed face down, then you shuffle the cards. After shuffling, all cards are left face-down.
Data Sources
Winr BT19-084 U LIBERATOR [Start of Your Main Phase] If you have face-up security cards, gain 1 memory. [Main] By suspending this Tamer, 1 of your Digimon may digivolve into a Digimon card in your face-up security cards. If this effect digivolved, you may place 1 Digimon card with the [Royal Base] trait from your hand face up as the bottom security card. --- [Security] Play this card without paying the cost.
Winr BT19-084 U LIBERATOR [Start of Your Main Phase] If you have face-up security cards, gain 1 memory. [Main] By suspending this Tamer, 1 of your Digimon may digivolve into a Digimon card in your face-up security cards. If this effect digivolved, you may place 1 Digimon card with the [Royal Base] trait from your hand face up as the bottom security card. --- [Security] Play this card without paying the cost.
Winr BT19-084 U LIBERATOR [Start of Your Main Phase] If you have a face-up security card, gain 1 memory. [Main] By suspending this Tamer, 1 of your Digimon may digivolve into a Digimon card in your face-up security cards. If this effect digivolved, you may place 1 Digimon card with the [Royal Base] trait from your hand face-up as your bottom security card. ---
サイキヨ BT19-084 U リベレイター 【自分のメインフェイズ開始時】自分の表向きのセキュリティがあるなら、メモリー+1。 【メイン】このテイマーをレストさせることで、自分のデジモン1体を自分の表向きのセキュリティのデジモンカードに進化させる。この効果で進化したなら、自分の手札から、特徴に「ローヤルベース」を持つデジモンカード1枚をセキュリティの下に表向きで置ける。 --- 【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。