Oko, Thief of Crowns's +1 makes an artifact or creature a 3/3 green Elk. Does that creature have summoning sickness, even if the creature it was transformed from did not?
Oko's name fixed for tags to work, and tags removed from the thread title, they don't work there. -MadMage
If an effect says a permanent "becomes" something (such as from Oko's second ability), the permanent affected by that effect remains the same permanent as before (see also C.R. 400.7 and this thread).
In general, a creature can attack, and its activated abilities with the tap or untap symbol in their costs can be activated, only if that permanent was under its controller's control continuously since their most recent turn began (C.R. 302.6). This is true regardless of whether that permanent was a creature when that player's most recent turn began.
For example, in general, if, during your turn—
a noncreature artifact enters the battlefield under your control, then becomes a creature in the same turn, that permanent can't attack this turn while it's a creature.
a noncreature artifact you controlled continuously since the turn began becomes a creature, that creature can attack as normal.
EDIT (Oct. 30): Edited after comment 4 was posted.
1) All objects (yes, all objects) get sick when…
-they enter the battlefield, or
-they change controller.
Nothing else causes sickness. Nothing. (no, not even that)
2) YOUR objects heal from sickness when YOUR turn BEGINS. (yes, when it actually begins. No, not even a few milliseconds later)
3) ONLY creatures care about being sick, unless they have Haste. (yes, an artifact creature is a creature nonetheless)
Oko's name fixed for tags to work, and tags removed from the thread title, they don't work there. -MadMage
In general, a creature can attack, and its activated abilities with the tap or untap symbol in their costs can be activated, only if that permanent was under its controller's control continuously since their most recent turn began (C.R. 302.6). This is true regardless of whether that permanent was a creature when that player's most recent turn began.
For example, in general, if, during your turn—
EDIT (Oct. 30): Edited after comment 4 was posted.
1) All objects (yes, all objects) get sick when…
-they enter the battlefield, or
-they change controller.
Nothing else causes sickness. Nothing. (no, not even that)
2) YOUR objects heal from sickness when YOUR turn BEGINS. (yes, when it actually begins. No, not even a few milliseconds later)
3) ONLY creatures care about being sick, unless they have Haste. (yes, an artifact creature is a creature nonetheless)
That's it!
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules