mtg mythic edition booster box War of the Spark Sets – Axion Now The Gathering Guilds of Ravnica Mythic Edition

If you choose not to cast the card, it remains in exile

This is just awesome

Thirsting Axe: The downside is really restrictive and I am not sure it is worth it, unless you meant to sacrific the creature anyway.

But Zell's ability has a drawback

The universal dilemma of the Infiltrator was that few decks that played it wanted to tap out to get him there, but sticking him on the board was so devastating that most opponents would consider themselves fortunate to spend that window of opportunity making him go away as trying to race him with a traditional three- or four-drop was pure folly and playing your own blocker, including your own Shadowmage or something a little bulkier risked a removal spell that would lead into a downward spiral of card disadvantage

Instead, this is a better addition for Sapphire/Steel