Arena's ability targets both a "creature you control" and a "creature of an opponent's choice they control" (C.R. 115.1c, 108.1). As you activate Arena's ability, the opponent can't choose a creature with hexproof they control as the second target, since it would then be a target of that ability (which you control), which is not allowed (C.R. 608.2c, 601.5, 601.2c, 702.11b, 113.8, 101.2).
Note that hexproof on a permanent means, "This permanent can't be the target of spells or abilities your opponents control" (C.R. 702.11b), not, say, "An opponent can't choose this permanent as a target of spells or abilities they control".
Arena's ability targets both a "creature you control" and a "creature of an opponent's choice they control" (C.R. 115.1c, 108.1). As you activate Arena's ability, the opponent can't choose a creature with hexproof they control as the second target, since it would then be a target of that ability (which you control), which is not allowed (C.R. 608.2c, 601.5, 601.2c, 702.11b, 113.8).
Note that hexproof on a permanent means, "This permanent can't be the target of spells or abilities your opponents control" (C.R. 702.11b), not, say, "An opponent can't choose this permanent as a target of spells or abilities they control".
Thank you! Now this is like the first time I see a downside on hexproof!
What happens if my opponent chooses a creature with hexproof? I presume my opponent chooses a creature, though Arena still targets it.
Shu Yun, the Silent Tempest WUR Voltron Control
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Note that hexproof on a permanent means, "This permanent can't be the target of spells or abilities your opponents control" (C.R. 702.11b), not, say, "An opponent can't choose this permanent as a target of spells or abilities they control".
Thank you! Now this is like the first time I see a downside on hexproof!
Shu Yun, the Silent Tempest WUR Voltron Control
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Hallar
Ulrich the Politician
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O-Kagachi, Mathas, Mairsil
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