I want cards that grant situational bonuses like hexproof, where it's a cost to include them, but they're not wasted if they're not used.
But specifically something unlike a cantrip, where you feel good for holding it until you need it, rather than for guessing whether you should get rid of it as soon as you have spare mana or not.
Hmm. Tricky. The life gain is a nice bonus, but it's bound to be a little underwhelming. I'd argue that might be a structurally better card, but then the hexproof instant would be awkward enough so that the card might not see play. Hm.
See Challenge # 153.
I want cards that grant situational bonuses like hexproof, where it's a cost to include them, but they're not wasted if they're not used.
But specifically something unlike a cantrip, where you feel good for holding it until you need it, rather than for guessing whether you should get rid of it as soon as you have spare mana or not.
Hmm. Tricky. The life gain is a nice bonus, but it's bound to be a little underwhelming. I'd argue that
might be a structurally better card, but then the hexproof instant would be awkward enough so that the card might not see play. Hm.
Rather than
"Gain half X life", wouldn't it make more sense to be 
"Gain X life"?
Anyway, I agree that the design thoughts are interesting.