Enchant creature
When Venarian Gold enters, tap enchanted creature and put X sleep counters on it.
Enchanted creature doesn't untap during its controller's untap step if it has a sleep counter on it.
At the beginning of the upkeep of enchanted creature's controller, remove a sleep counter from that creature.
The counters are placed on the creature to which it enters attached. If you later move Venarian Gold to a different creature, the counters remain on the original creature and no counters are put on the new creature.