Shadow rift on a percursor Golem is 12 damage, nigh unblockable, and an ancestral. I have read everyones arguments, but am not sure myself yet, but if this does affect all golems, then shaodw rift + precursor + lodestone = 19 damage, and 4 cards for 1 mana. This does not seem bad to me.
Precursor Golem

Artifact Creature -- Golem
3/3
When Precursor Golem enters the battlefield, put two 3/3 colorless Golem artifact creature tokens onto the battlefield.
Whenever a player casts an instant or sorcery spell that targets only a single Golem, that player copies that spell for each other Golem that spell could target. Each copy targets a different one of those Golems.
* The second ability triggers whenever a player casts an instant or sorcery spell that targets only one Golem. That Golem can be Precursor Golem itself, one of the Golem tokens it created, or any other Golem. It doesn't matter who controls the Golem.
From the SOM FAQ: http://www.wizards.com/dci/downloads/EN_MTGSOM_FAQ_20100922.rtf

: Add X or Y to your mana pool.