No, I don't think there's evasion based on mana value, other than a handful of cards with protection. I think SI was referring to daunt, green's "power 2 or less" evasion

I just realized that you meant the mechanic flying when asked if aerial creatures implicitly have flying. Flavorfully, aerial creatures implicitly have flying, but there no mechanical relation or connection between the aerial supertype and the ability flying.

• "Return target non-aerial, non-aquatic creature an opponent controls to its owner's hand. Each opponent mills four cards."

That's totally an option.

So is:

• "When you cast ~, each opponent mills four cards.
  Return target non-aerial, non-aquatic creature an opponent controls to its owner's hand."

So what's the point of the "bonus action", then? You are checking for the same criteria as with the targeting restriction and make a seven-line common.

I want the mill as the first action and the bounce as the bonus action (or at least I think I did, as I didn't save the original wording).

I also feel I wanted the card formatted more towards multiplayer, or at least expected the card to be there, were the milling is better targeting all players and probably fine at the cost. Bounce could be okay as a bonus action here, since there's no guarantee other players won't have aquatic or aerial cards milled. seems too cheap for "Return target creature each opponent controls. Each opponent mills four cards."

This is still a very complicated way to make a bounce spell.

Is this effect really worth seven lines of text over:

• "Return target non-aerial, non-aquatic creature to its owner's hand. That player mills four cards."

at ?

you forgot to remove "of the same".

"greater mana value" is open towards the top, which is not usually a restriction you would see. The design seems "dirty" tome in the way it seems to aim at giving you a restricted Show and Tell or Dramatic Entrance, but also uses the "drawback" of allowing the same to an opponent, except there are a lot of cases where itdoesn't work for them.

Why not simply "with a different name" rather than "with a greater mana value"? What is the grand plan on getting the opponent on board anyway? What about creatures without supertypes; are they excluded on purpose?

I feel this design gets worse due to its self-imposed linearity.

The word "type" here is ambiguous. As written, it's implied you mean (creature sub)type, as in Soldier, Beast, etc.

I'd rewrite as such: "Each player who returned a creature to their hand this way may put a creature card of the same that shares a supertype with it, and with a greater mana value from their hand onto the battlefield. (Aerial and Aquatic are supertypes)"

There's probably a way to merge this second sentence with the first one to avoid repetition and make it shorter, dunno.

New dunkleosteus info dropped, and now I look like a clown for making this.
Source: Engelman paper

The wording is ambiguous - or at least a garden path phrase. I think you want "For each player, if neither [...] into that player's graveyard [...]".

Actually, it might be even better to say "When a player is milled this way, if neither" etc. because that way you don't need all the legal targets upon casting the spell.

This is intended to work so that the aerial and aquatic supertypes can return a mana value card to put out a higher mana value one. However, I don't know if supertypes count as a card type. If they do not, I'd be willing to just sighs simplify this to just "creature."