Intruder Alarm

Creatures don't untap during their controllers' untap steps.
Whenever a creature enters the battlefield, untap all creatures.

Royal Assassin

Thornbite Staff

Equipped creature has "{2}, {T}: This creature deals 1 damage to any target" and "Whenever a creature dies, untap this creature."
Whenever a Shaman creature enters the battlefield, you may attach Thornbite Staff to it.
Equip {4}

Frozen Aether

Artifacts, creatures, and lands your opponents control enter the battlefield tapped.

King's Assassin

{T}: Destroy target tapped creature. Activate only during your turn, before attackers are declared.