Invasion of Alara
Playing on the Android app, opponent played Invasion of Alara, and cast both of the creature spells retrieved by the ETB ability (Doomskar Warrior and Thrashing Frontliner). For the rest of the match I was unable to select those two cards for any purpose: couldn't long-press to see the card details, block their attacks, or target them with spells.
Unfortunately, I didn't get a screenshot, but the affected cards had a faint, persistent visual effect - a bit of an orange glow. Not something I recognized as associated with any particular mechanic, but maybe some (normally) transient thing associated with exile or something.
No log file because I cannot find any documentation on how to make one on Android.