Because Mowu's replacement effect affects only Mowu, it will apply if Mowu somehow enters the battlefield with one or more +1/+1 counters on it and give Mowu an additional +1/+1 counter
If you're going to use this card on its own, I would recommend putting it into the active Pokemon spot early in the game and using Rain Splash most turns while getting stronger Pokemon set up on your bench
In normal circumstances, the green dot test will still help you confirm a cards authenticity
Additionally, it should be noted that you can use Pack Points via the Pack Point Exchange function on the pack opening screen to earn these cards, though it's really only there for badluck protection because it costs a whopping 1500 Pack Points to get only one of the Immersive Art Cards
Fortunately for new players, in Lorcana, there is only one format and one set available, so the meta is easier to digest
V was still a vast improvement from the GX ones