When Corruption of Towashi enters, incubate 4. Whenever a permanent you control transforms or a permanent you control enters transformed, you may draw a card. Do this only once each turn.
2023-04-14
Once you've chosen to draw a card because of the last ability (which is likely as soon as possible, but there may be situations in which you don't want to draw immediately), that ability will stop triggering for the duration of that turn.
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Only a transforming double-faced permanent can enter the battlefield "transformed," and only if it enters with its back face up. Notably, melded permanents can't enter transformed, and modal double-faced permanents can't enter transformed, even if they enter with their back faces up.
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Similarly, only transforming double-faced permanents (including transforming double-faced cards and Incubator tokens) can transform. A face-up permanent turning face down doesn't count as transforming, nor does a face-down permanent turning face up.
2023-04-14
The last ability of Corruption of Towashi will trigger if a permanent you control transforms in either direction, going from front face up to back face up or vice versa.