Nissa, Vital Force, Kalonian Hydra, Wolfir Silverheart, and even Whisperwood Elemental are all decent options in the deep deep five slot
You still want to get in as much combat damage in the early game as you can, even if your opponent will eventually put together too many large blockers for you to clear away
Leonardo, Sewer Samurai | 3 Colorless Mana, 1 White Mana Legendary Creature Mutant Ninja Turtle Samurai Sneak 2 Colorless Mana, 2 White Mana (You may cast this spell for 2 Colorless Mana and 2 White Mana if you also return an unblocked attacker you control to hand during the declare blockers step
Its an instant, and unless youre the unfortunate victim of a Tormods Crypt, youll be happy
, : This creature fights another target creature
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