Silco, the Chembaron

Skulk, Vigilance
Whenever Silco, the Chembaron enters the battlefield or attacks, create a Shimmer token attached to target creature of your choice. The cumulative upkeep cost for creatures you control enchanted with Shimmer is reduced by {3}. This cannot reduce the cost below {0}.
If a permanent one of your opponents control would
be sacrificed due to cumulative upkeep, remove all
age counters from that permanent and gain control
of it instead.