So, I'm thinking of making a field spell that supports the Junk archetype, and I was wondering if it's any good

Junkyard Castle
Field Spell
While this card is face-up on your side of the field, "Junk" monsters cannot be targeted by card effects. Once per turn, you may target one "Junk" monster you control, and if you do, the targeted monster gains 200 ATK for every "Junk" monster in your GY until the end of your turn. You can only activate this effect of "Junkyard Castle" once per turn.