So, I don't think this card is really vintage playable, although it is really cute and perhaps has angles to shoot. (Kismet on legs! Stasis is back BABY).
No, the reason I posted this is because this forum has some of the most intelligent folks in Magic, and I'm very unclear on how this works from a rules perspective. The question for me is what happens when you have Archelos out and play something that ETB tapped like, say, a Guildgate. Both cards have text directing the card to enter the battlefield tapped or untapped. So, what happens?
Assuming they are both replacement effects, I think the answer is that the card MUST enter the battlefield untapped. Rule 616.1 says that if two replacement effects try to apply, normally the player controlling the permanent being effected chooses. But, if one of the effects is on the effected card itself, then the self-replacement effect must be applied first. Rule 614.15. So, the Guildgate's own ability tells it to enter tapped, and then the Turtle's tells it to enter untapped, and so the latter one controls.
But, it's not clear to me that these are replacement effects at all. They're not written in the form "If a permanent would X instead it Ys." Has anyone encountered this before?
Note that some cards like Thalia don't raise this issue because cards traditionally do not say "This card ETB untapped" in their card text, so there is no conflict between effects to resolve.