If one of the creatures is an illegal target and the other one isn't as The Earth Crystal's last ability tries to resolve, the original distribution of counters applies and the counter that would have been put on the illegal target is lost
But let us get serious: what are you going to do with churning out 1/1 creatures
This all adds up to making this a lot lot better than Introduction to Prophecy, even if it is still a little bit underwhelming
Number 25 Language English Not Legal Formats Alchemy, Brawl, Commander, Competitive Brawl, Historic, Legacy, Modern, Pauper, Pioneer, Standard, Timeless, Vintage
You can pay one black mana and sacrifice another creature to have a player mill three cards, which is cool, but you can also pay one life to add one colorless mana which can only be used to cast spells from your graveyard
Since the beginning of Magic, it has remained consistent that you can only tap untapped permanents and untap tapped ones