Tyrannical Pitlord

Flying, trample
As this creature enters, choose another creature you control.
The chosen creature gets +3/+3 and has flying.
When this creature leaves the battlefield, sacrifice the chosen creature.

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Flying, trample
As Tyrannical Pitlord enters the battlefield, choose another creature you control.
The chosen creature gets +3/+3 and has flying.
When Tyrannical Pitlord leaves the battlefield, sacrifice the chosen creature.

If Tyrannical Pitlord enters the battlefield at the same time as another creature, that creature can’t be chosen.

If Tyrannical Pitlord’s leaves-the-battlefield triggered ability resolves while its controller is not the same as the controller of the chosen creature, that creature will not be sacrificed.

If another player gains control of the chosen creature while Tyrannical Pitlord is still on the battlefield, that creature will continue to have flying and get +3/+3.

If the chosen creature leaves the battlefield, you can’t choose a new creature.

The ability of Tyrannical Pitlord that allows you to choose a creature isn’t a triggered ability and doesn’t use the stack. Players can’t respond to your choice of which creature it’s affecting.