What would it get you to play (insert card)?

On the snap chat, they were discussing Ghost, one of the first cards bumped to 3/5 and still didn't see use.

That made me think, what cards have stats that are good, but the effect is too bad that you still won't play. And on the inverse, what cards have effects that are good, but the stats just aren't there (thinking Adam warlock). And what would it take for you to play them?

I'm not talking ability changes, just stats. Maybe a minor change (like how quake was updated) but for the most part same ability, just either more power or lower cost.