Nivmagus Elemental’s ability is an activated ability that exiles an instant or sorcery spell you control from the stack… only instants or sorceries. This does not allow you to exile activated or triggered abilities on the stack (e.g., Planeswalker abilities, artifact abilities, etc.).

While most abilities can be activated any time you could cast an instant, that doesn’t mean they are instant spells, and abilities that say you can only activate them when you could cast a sorcery are not sorcery spells.

Today’s Rules Tip written by Nick Rutkowski, Level 2 judge from El Cerrito, CA