Quote from the_jevry »you can however sacrifice the creature during the end step before your turn begins since there isn't a tap ability involved (like svannahlion said, this is assuming reccuring nightmare somehow isn't restricted to sorcery speed)
Quote from Comp Rules »508.4. If a creature is put onto the battlefield attacking, its controller chooses which defending player or which planeswalker a defending player controls it’s attacking as it enters the battlefield (unless the effect that put it onto the battlefield specifies what it’s attacking). Such creatures are “attacking” but, for the purposes of trigger events and effects, they never “attacked.”
Quote from Comp Rules » 706.4. Some effects cause a permanent that’s copying a permanent to copy a different object while remaining on the battlefield. The change doesn’t trigger enters-the-battlefield or leaves-the-battlefield abilities. This also doesn’t change any noncopy effects presently affecting the permanent. Example: Unstable Shapeshifter reads, “Whenever a creature enters the battlefield, Unstable Shapeshifter becomes a copy of that creature and gains this ability.” It’s affected by Giant Growth, which reads “Target creature gets +3/+3 until end of turn.” If a creature enters the battlefield later this turn, Unstable Shapeshifter will become a copy of that creature, but it will still get +3/+3 from the Giant Growth.
Quote from Comp Rules »616.1. If two or more replacement and/or prevention effects are attempting to modify the way an event affects an object or player, the affected object’s controller (or its owner if it has no controller) or the affected player chooses one to apply, following the steps listed below. If two or more players have to make these choices at the same time, choices are made in APNAP order (see rule 101.4).
616.1b If any of the replacement and/or prevention effects would modify under whose control an object would enter the battlefield, one of them must be chosen. If not, proceed to rule 616.1c.
616.1d Any of the applicable replacement and/or prevention effects may be chosen.
616.1e Once the chosen effect has been applied, this process is repeated (taking into account only replacement or prevention effects that would now be applicable) until there are no more left to apply.