In case you didn't play the original Ravnica block, here's a refresher for what this keyword mechanic means:
"For each colored mana in this spell’s total cost, you may tap an untapped creature of that color you control rather than pay that mana. For each generic mana in this spell’s total cost, you may tap an untapped creature you control rather than pay that mana."
Essentially then, Convoke allows you to significantly reduce the cost of a spell if you have several untapped creatures in play. This doesn't change the casting cost of the spell, but merely reduces the amount of mana you actually have to pay. This can even reduce the cost down to zero.
One of the more popular Convoke cards in Pauper was the spell Scatter the Seeds:
Since the original Ravnica was released, the token-generating effect has become more predominantly White rather than Green. And as I will discuss next time, that explains why Magic 2015 brings us a very similar card but now in White.
What do you think of Convoke as a returning ability? Let me know in the comments below.