One sided wraths are always good, and to have a blue one not tied to Krakens, Leviathan et al is refreshing
You can think about Lightning bolt, that can be used as a removal or a burn spell, depending on the situation
In the case of the Opportunist, you basically get a delayed copy of the second spell you cast in a given turn
Halvar, God of Battle is a beater for a good rate that can really shine in an equipment-focused deck
This is a very powerful card even when played for its full cost since exiling is the best removal type, especially in a format like Pioneer where abilities like indestructible are more prevalent
Thalia, Heretic Cathar is just a one-of, but it offers some nice value, taxing both creatures and land