What happens if there is both a tapped and untapped Archelos, Lagoon Mystic on the battlefield? (Commander Legends spoilers)
These would be 2 different replacement effects, so the player whose permanent is entering the battlefield would choose one to apply first, and would then apply the other (so only the second one they chose would end up mattering):

614.1d Continuous effects that read “[This permanent] enters the battlefield . . .” or “[Objects] enter the battlefield . . .” are replacement effects.


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.



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.