So I was participating in an Old School tournament and ran into an issue. My opponent activates his Chaos Orb and chooses my only basic land, so in response I tap it for mana. He claims that once he's chosen the target that it's too late for me to respond.
In reading the oracle text and rulings I find nothing to corroborate his call. We were playing Eternal Central rules, here's their errata:
"Chaos Orb
2
Artifact
1, Tap: Choose a nontoken permanent on the battlefield. If Chaos Orb is on the battlefield, flip Chaos Orb onto the battlefield from a height of at least one foot. If Chaos Orb turns over completely at least 360 degrees during the flip, and lands resting on the chosen permanent, destroy that permanent. Then destroy Chaos Orb.
(Note: because of how Chaos Orb is worded, with it being destroyed after a flip, it can still be Disenchanted or Shattered in response to the activation, which will nullify the ability to flip, since it is no longer on the battlefield. This is consistent with the wording of Chaos Orb not being sacrificed upon activation, as it probably would with modern templating. Also note that Chaos Orb chooses, but does not target.)"
So was my opponent correct, or was he just misinformed?
According to that text, the choice happens on resolution, not on announcement (it's not targeted). If you want to respond, you would have to do so before the ability resolves (and before knowing what permanent they'll choose), not after. They might make their choice know before the ability resolves (in which case, they'd be locked in to that choice unless you respond to the ability), but otherwise, you'll have to respond without knowing what they'll be choosing.
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DCI Level 2 Judge
Scientists have calculated that the chance of anything so patently absurd actually existing are millions to one. But magicians have calculated that million-to-one chances crop up nine times out of ten.
With the understanding that the Oracle text of Chaos Orb is different from the text you cited (C.R. 108.1), the ability that you give in comment 1 doesn't target anything (it lacks the word "target", for example) (C.R. 115.1c; see also C.R. 115.10a); thus if a player activates that ability, other players generally won't know which nontoken permanent will be chosen until that ability resolves (C.R. 608.2d). In general, however, if the player activating that ability does choose a nontoken permanent in advance, they will be bound to that choice unless another player intervenes (for situations other than sanctioned tournaments, see C.R. 722.2a-c).
Likewise, Chaos Orb's ability, as given in its Oracle text, doesn't target anything either (C.R. 115.1c, 108.1).
EDIT (Apr. 25): Edited, because some rules were renumbered in the meantime.
In reading the oracle text and rulings I find nothing to corroborate his call. We were playing Eternal Central rules, here's their errata:
"Chaos Orb
2
Artifact
1, Tap: Choose a nontoken permanent on the battlefield. If Chaos Orb is on the battlefield, flip Chaos Orb onto the battlefield from a height of at least one foot. If Chaos Orb turns over completely at least 360 degrees during the flip, and lands resting on the chosen permanent, destroy that permanent. Then destroy Chaos Orb.
(Note: because of how Chaos Orb is worded, with it being destroyed after a flip, it can still be Disenchanted or Shattered in response to the activation, which will nullify the ability to flip, since it is no longer on the battlefield. This is consistent with the wording of Chaos Orb not being sacrificed upon activation, as it probably would with modern templating. Also note that Chaos Orb chooses, but does not target.)"
So was my opponent correct, or was he just misinformed?
Scientists have calculated that the chance of anything so patently absurd actually existing are millions to one. But magicians have calculated that million-to-one chances crop up nine times out of ten.
Likewise, Chaos Orb's ability, as given in its Oracle text, doesn't target anything either (C.R. 115.1c, 108.1).
EDIT (Apr. 25): Edited, because some rules were renumbered in the meantime.
Thanks for the clarification though.