Q1: What does a card with "X in its text" refer to?
It refers to a card that contains the specified text or icon in its name, traits, effects, inherited effects, (Rule), digivolution requirements, DNA digivolution, DigiXros requirements, burst digivolve, App Fusion, or Link. For example, a card with Knightmon in its text would include cards with the name DarkKnightmon and cards with the text Knightmon in their effects.
Q2: If I use this card's Start of Your Main Phase effect to place a card under a Tamer with cards under it, in what order do I place the card?
The card is placed on the bottom of the cards under the Tamer.
Tagiru Akashi BT21-088 SR Hunter/Hero [Start of Your Main Phase] By placing 1 Digimon card with <Save> in its text or the [Hero] trait from your hand under this Tamer, <Draw 1> and gain 1 memory. [Your Turn] When any of your Digimon would digivolve into a Digimon card with <Save> in its text or the [Hero] trait, by suspending this Tamer and placing 1 card from under your Tamers as any of their bottom digivolution card, reduce the digivolution cost by 1. --- [Security] Play this card without paying the cost.
Tagiru Akashi BT21-088 SR Hunter/Hero [Start of Your Main Phase] By placing 1 Digimon card with <Save> in its text or the [Hero] trait from your hand under this Tamer, <Draw 1> and gain 1 memory. [Your Turn] When any of your Digimon would digivolve into a Digimon card with <Save> in its text or the [Hero] trait, by suspending this Tamer and placing 1 card from under your Tamers as any of their bottom digivolution card, reduce the digivolution cost by 1. --- [Security] Play this card without paying the cost.
Tagiru Akashi BT21-088 SR Hunter/Hero [Start of Your Main Phase] By placing 1 Digimon card with <Save> or the [Hero] trait from your hand under this Tamer, <Draw 1> and gain 1 memory. [Your Turn] When any of your Digimon would digivolve into a Digimon card with <Save> or the [Hero] trait, by suspending this Tamer and placing 1 card from under your Tamers as any of their bottom digivolution card, reduce the digivolution cost by 1. ---