Mana Echoes

Oracle Text

Whenever a creature enters the battlefield, you may add an amount of C to your mana pool equal to the number of creatures you control that share a creature type with it.

Card Rulings

10/4/2004 You either get zero mana or all the mana. You can’t choose an amount in between.
10/4/2004 You do get to count the creature itself, you even get one mana if it is the only creature you have on the battlefield (assuming it has at least one creature type).