Q1: If Marcus Damon is treated as a Digimon by this card's effect and then its DP is reduced to 0 by an effect, is it deleted?
Yes, it's deleted.
Marcus Damon BT17-087 R [On Play] Until the end of your opponent's turn, 1 of your [Marcus Damon]s is also treated as a 3000 DP Digimon, can't digivolve and gains <Blocker>. [All Turns] When this Tamer becomes suspended, 1 of your Digimon gets +3000 DP for the turn. If you have a Digimon with [Agumon] or [Greymon] in its name, gain 1 memory. --- [Security] Play this card without paying the cost.
Marcus Damon BT17-087 R [On Play] Until the end of your opponent's turn, 1 of your [Marcus Damon]s is also treated as a 3000 DP Digimon, can't digivolve and gains <Blocker>. [All Turns] When this Tamer becomes suspended, 1 of your Digimon gets +3000 DP for the turn. If you have a Digimon with [Agumon] or [Greymon] in its name, gain 1 memory. --- [Security] Play this card without paying the cost.
Marcus Damon BT17-087 R [On Play] 1 of your [Marcus Damon] is also treated as a 3000 DP Digimon that can't digivolve and gains <Blocker> until the end of your opponent's turn. [All Turns] When this Tamer becomes suspended, 1 of your Digimon gets +3000 DP for the turn. If you have a Digimon with [Agumon] or [Greymon] in its name, gain 1 memory. --- [Security] Play this card without paying the cost.
大門大 BT17-087 R 【登場時】相手のターン終了まで、自分の「大門大」1体はデジモン• DP3000としても扱い、進化できず、≪ブロッカー≫を得る。 【お互いのターン】このテイマーがレストしたとき、ターン終了まで、自分のデジモン1体をDP+3000。名称に「アグモン」/「グレイモン」を含む自分のデジモンがいるなら、メモリー+1。 --- 【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。