Q1: What exactly does this card mean when it says "when leaving the Battle Area"?
When leaving the Battle Area" refers to when this Digimon is "placed in trash," "returned to hand or deck," "placed in security," "moved to the Breeding Area," or "placed under another card."
Lv.4 Shoutmon X4 BT19-010 C Champion | Data | Composite/Xros Heart [All Turns] When this Digimon would leave the battle area, you may place up to 3 Digimon cards with the [Xros Heart] trait from this Digimon's digivolution cards under 1 of your Tamers. DigiXros -2: [Shoutmon]×[Ballistamon]×[Dorulumon]×[Starmons] When this would be played, you may place specified cards from your hand/battle area under it. Each one reduces the play cost.
Lv.4 Shoutmon X4 BT19-010 C Champion | Data | Composite/Xros Heart [All Turns] When this Digimon would leave the battle area, you may place up to 3 Digimon cards with the [Xros Heart] trait from this Digimon's digivolution cards under 1 of your Tamers. DigiXros -2: [Shoutmon]×[Ballistamon]×[Dorulumon]×[Starmons]
Lv.4 シャウトモンX4 BT19-010 C 成熟期 | データ種 | 合成型/クロスハート 【お互いのターン】このデジモンがバトルエリアを離れるとき、このデジモンの進化元から、特徴に「クロスハート」を持つデジモンカード3枚までを自分のテイマー1体の下に置ける。 「シャウトモン」x「バリスタモン」x「ドルルモン」x「スターモンズ」 登場するとき、手札/バトルエリアからこのカードの下に置ける。1枚ごとに登場コストをマイナスする