The astropath collapsed, his empty eye sockets aglow. He spoke three words before falling lifeless to the ground: "They . . . are . . . coming!"

Shadow in the Warp

The first creature spell you cast each turn costs {2} less to cast.
Whenever an opponent casts their first noncreature spell each turn, this enchantment deals 2 damage to that player.

Warhammer 40,000 Commander

The first creature spell you cast each turn costs {2} less to cast.
Whenever an opponent casts their first noncreature spell each turn, Shadow in the Warp deals 2 damage to that player.

Both the first and last abilities of Shadow in the Warp take into account spells cast before it was on the battlefield. For example, if an opponent cast a noncreature spell before it was on the battlefield, then casts a noncreature spell after it is put on the battlefield, Shadow in the Warp's second ability won't trigger because that is the second noncreature spell they've cast that turn.