He can generate Saproling tokens at will, provided you have the mana to spare, and the incidental life gain he provides can keep you alive even against highly aggressive opponents
It's estimated that only 36 such cards exist in the world today which is equal to the number of participants that took part in that year's world championships
Though that is of course a significant amount of money for a single card, its a very far cry from the 10k+ of its most expensive version
Being an instant, it also lets you set up key cards right before beginning your turn, including ramp like Sol Ring, shenanigans with Vedalken Orrery, or the ability to attack or tap with an artifact creature on your turn that would normally have to wait through a full turn cycle of summoning sickness
As it would happen a lot, it had to be something small that over time could turn into something big
Xerosic has the added benefit of giving players the choice of choosing either a Special Energy or a Tool card