The -2/-2 on turn thee will be good enough most of the time (in the current metagame), but hitting the life gain requirement isn't difficult (it is automatic if you run Ancient Cornucopia)
If you run Temur Sabertooth as a way to bounce Nikya to your hand, you could find yourself dropping an Eldrazi Titan on the back of a big Electrodominance or just bringing the table to its knees with an old fashioned Comet Storm
As such, cards that are very situational or that can be bad even if all players take the offer wont make the list
We have ramp, lifegain, draw, discard, creature and planeswalkers removal that you can scale, and an ultimate that is fairly quickly reached
But whatever card you think fits that description, these cards somehow cost even more (unless youre thinking of one on this list, of course)
See why the enchantment was added