Struggling with Spurn

This card I made is terrible and I'm not using it, but I'm posting to highlight some of the problems I'm having trying to design with the spurn mechanic.

As I'm trying to design around spurn in white, it feels like white wants to use spurn to punish aggressive combat tricks. That's what it does in combat at instant speed. Kill an attacker; call in token blockers. Essentially punish players for coming at them.

But timing is a problem with this card, and that's bad, because the whole point of spurn is to reward smart timing when casting instant-speed spells. Experienced players will likely wait until after blockers are declared to deploy combat tricks. At that point, if you respond with Defense of the Arbor, then it's too late to use the creature tokens as blockers. They're not worthless, but they're not going to accomplish what I envision happening. This isn't really "rewarding good timing."

I tried a version where I reversed the effects and dropped the cost down.

This is terrible. Can you imagine looking at this card in a limited format and realize it might not even destroy a creature? No, it's terrible.

I think spurn is going to be a good tool to respond to removal and damage, but the way the mechanic is written right now is not going to be great in combat itself.

The first card could potentially be fixed by setting it to kill a "big creature," which is in white's wheelhouse and that kind of removal is most certainly going to be in the set. But I'm not sure of the value of stapling spurn onto it.

I'm also worried that the mechanic is actually terrible for a limited environment where players are focused on creatures and play only a limited number of non-creature spells. These spells must be designed so that they're playable even if you don't get the spurn trigger. The mechanic needs to feel like a reward. If you feel like you're going to lose the game because you cannot trigger the spurn effect, that's a bad card.

In that vein, I just realized that the drumbeat enchantment cycle cannot exist in the same set as spurn as the mechanic is now. If I use those enchantments instead of auras, then suddenly spurn loses a whole bunch of things to respond to. The irony of spurn is that its value as a mechanic is based on having strong non-creature spells to react to. If I don't have those, spurn is a weirdly inessential component to the set.