When activating the quick effect of Hecahands Xeno, its resolution always successfully reveals two cards from the extra deck, but it will sometimes skip over the prompt to special summon, even if one or both are legal targets. As far as I am aware there shouldn’t be anything stopping the special summon from occurring; other than the prompt simply not appearing. Much of the time the ability resolves normally, but seemingly arbitrarily the prompt to special summon won’t appear.
Discovered on testing: the issue doesn’t trigger if Mankibuel + 2 hecahands is in the starting hand, only when the lines to bring out Xeno are actually played. Other than this I haven’t found any consistency with what triggers it.
During the below replay, Xeno successfully revealed two extra deck monsters, however no prompt to summon either appeared; the chain/activation ended with the reveal alone.
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