How about changing it to a normal spell card, and the monster to something like "This card can only be special summoned by the effect of "Spell's name""
Waterproof Protection: Made of PP plastic to protect cards from falling out and water damage
This mechanic is very similar to how charge counters were used in the Scars of Mirrodin block, where you could have diverse implementations in cards like Shrine of Burning Rage, Tangle Wire, and Lux Cannon
Modern Horizons 3 contains the 5 basic lands (Plains, Island, Swamp, Mountain, and Forest) with variant treatments, plus an uncommon Snow-Covered Wastes (included as one of the 101 uncommons) with its variant treatments
It produces three mana of any color for zero cost, which makes it the most powerful mana acceleration ever printed
[2] Once per chain, up to thrice per turn (Quick Effect): You can target 1 face-up monster your opponent controls