Urtet, Remnant of Memnarch

Whenever you cast a Myr spell, create a 1/1 colorless Myr artifact creature token.
At the beginning of combat on your turn, untap each Myr you control.
{W}{U}{B}{R}{G}, {T}: Put three +1/+1 counters on each Myr you control. Activate only during your turn.

Jinxed Choker

At the beginning of your end step, target opponent gains control of this artifact and puts a charge counter on it.
At the beginning of your upkeep, this artifact deals damage to you equal to the number of charge counters on it.
{3}: Put a charge counter on this artifact or remove one from it.