Blim does not have summoning sickness and cannot be blocked by an opponent.
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Notable Prerequisites
You control a face-down creature whose front face is a permanent card.
Steps
Donate
Karlov Watchdog to an opponent.
During the opponent's turn, activate
Phantom Train by sacrificing a face-down creature you control.
When the creature dies,
Yarus's second ability triggers, returning it from your graveyard to the battlefield face-down as a 2/2 creature, and then not turning it face-up due to