My opponent has 4 untapped forests and taps all their land to cast Thrun.
I respond by using Quicksilver Amulet to put Lodestone Golem into play. Since Thrun now costs an extra
1 that my opponent does not have, would it be countered? Would the result be any different if the spell being cast did not have Thrun's ability (perhaps it was a Cudgel Troll instead)?
For Thrun, it seems like this might be a case of "countered by game rules" but it doesn't say "can't be countered by spells or abilities" it just says "can't be countered."