CardName: Eldest Thief
Cost: 3{U}
Type: Creature - Human Advisor Rogue
Pow/Tgh: 3/3
Rules Text: Flash
{2}{W/B},{T}: Exile target tapped creature. If you own that
card, you may return it to the battlfield at the beginning
of your next endstep.
Flavour Text:
Set/Rarity: Washikow Mythic
Eldest Thief
M
Creature – Human Advisor Rogue
Flash
,: Exile target tapped creature. If you own that card, you may return it to the battlfield at the beginning of your next endstep.
Since you exile it first, I don't think you can control it when the second part checks. Maybe "if you own that card" instead?
followed dude1818's suggestion