Nope. When a creature changes control, it becomes summoning sick, but it never left or entered the battlefield. Riku only triggers on permanents entering the battlefield, meaning they have to come from somewhere else.
No. Control effects don't cause the creature to change zones. There is only one battlefield zone. The physical arrangement generally indicates who controls which permanents, but doesn't actually mean anything to the game.
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Level 3 Judge
This FAQ answers many of the common questions asked in the MTGS Rulings forum. Take a look!
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