Artifacts that do nothing without a colored mana are a no go. So Frostmage Heirloom should work more like Neurok Stealthsuit. To accomplish this you may have to remove the +1/+1 bonus. Though at that point it seems odd that its an equipment.
Worldbend doesn't work the way you may think it does. With the way its worded you choose the player and permanent, then you get up to three un/tap choices depending on what is exiled. It seems you want this to un/tap up to three permanents if this is what you intended the easiest way is to drop the targeting on the permanents otherwise the wording will get very cluttered.
Other than that I would like to echo everything alwaysatoad said, very interesting designs and they pointed out the majority of the problems.
They moved Ajani out of mono-white because they wanted to cut the number of mono-white walkers, they could have done the same to Gideon, though to red not green, but something made them choose Gideon over Ajani for the Gatewatch and if it isn't popularity then who knows, but they are the only ones who would know. Its fine that you 'think' the others aren't as popular but Wizards makes these decisions with the actual data so its possible they didn't choose the 5 more popular mono-color walkers but that seems incredibly unlikely. Personally each of the Gatewatch members falls into the bottom half on favorite planeswalkers but I doubt that my thoughts are in the majority.
The main problem is they have repeatedly said they have no intention of allowing nonplaneswalkers the ability to planeswalk. Because it kind of defeats the purpose of being a planeswalker. This portal has the very significant drawback of destroying organic matter that passes through, and while Tezzeret is obviously building a portal to use for something, he is building a PORTAL not a device that would allow a ship to planeswalk but a stable single portal.
Phyrexian mana makes it French vanilla masquerading as vanilla. Think of it like this.
Phyrexian Avatar (Mythic) WUBRG
Creature - Avatar
10/10
Each 2 life you pay while casting Phyrexian Avatar pays for W, U, B, R, or G.
You're confusing French Vanilla with Virtual Vanilla. French Vanilla is a creature with only keyword abilities. While Virtual Vanilla is a vanilla after the turn its been played. Maro has said it might have reminder Text so while techinally a Vanilla it could still have some thing like Phyrexian Mana with the reminder text telling you how the card is played.
5 color Phyrexian 13/13
5cmc, one of each color, but all Phyrexian
obviously this would be absolutely broken in half, but it is the only way I have thought of for a vanilla to feel mythic
This is interesting because while obviously broken, if they use some other new type of mana they could probably get a mythic feel while still being vanilla. This seems the most likely of everything mentioned here. Though the actual p/t to mana cost could be anything.
I believe it was mentioned somewhere that there was a RG god a long time ago until they were killed/disappeared.
Maro and Doug have each commented that there wasn't a RG god during and right before Theros, but if one existed it was a long time ago, long enough for people to have completely forgotten.
Deep Slumber is a strong card that you have added 'draw a card' and probably pushed it over the limit. Hitting your own creatures is enough for Sleep to cost 1 less(debatably), but 1 less and draws you a card. That's over the top.
Reynol, Master Magus is interesting and annoying as all hell. His ability should be 'When you cast' not 'If you cast' look at the Eldrazi to see non conditional cast triggers.
Rez, Explorer of Realms's +1 may be fine putting the land into play. It is conditional card advantage but it only gets lands so into play should still be safe. Maybe into play tapped. That -2 isn't very strong even if the + is putting lands into your hand, certainly getting 2 Summer Blooms for 3 mana is insane but it happens over 3 turns so its rather underwhelming and requires other cards putting extra lands into your hand to really function. The ultimate seems disconnected from the other abilities. It still references lands but only as the modifier on its +/+, it might be better if this animated your lands or in someway made your lands better.
You're quite correct, this looks a lot like creature types. My thinking is that:
a) Any mechanic that 'tags' permanent objects with an open set of strings and does simple if/then operations on the strings is going to look a lot like subtypes because that's what subtypes do.
b) Subtypes can accomplish this at a cost: There's already a big, problematic set of cards (changelings) that have all creature subtypes.
c) I didn't use this effect here, but unlike subtypes, names can operate regardless of permanent types.
d) Subtypes have a clear connotation of, 'This is an example of (type)' whereas names don't necessarily have to have that connotation, or they can have much more specific connotations (like Mellunite above, an inappropriate creature type but acceptable name.)
I figure this only works in Constructed unless you really push hard for Limited themes because you need a certain (high) saturation of cards for name mechanics to work in a visible way.
If you don't want it to be creature types, then find a reason so it has to be something else. The easiest way is to make noncreatures with this and make sure they matter. Every card you showed would work better if they were rebels and affected other rebels(you can replace rebels with your chose of 'class' creature type). Changelings aren't a reason to forgo new tribal interaction, unless you are making a new tribe that is inherently broken. You can do what Astrolabe said and put a semi-meaningless marker on your cards via a keyword like Devoid and then reference it whenever you want, like on Corrupted Crossroads.
For the whole constructed vs limited, your idea is almost exactly tribal. It isn't hard to push tribal up to the numbers needed to be relevant in limited, look at Tarkir. There was a Semi-meaningful warrior tribal element to limited without saturating the set with warriors and that was without it even being a theme or mechanic of the set.
Other than Internment, which becomes significantly over powered, how does this benefit from not simply being creature types? Its possible you'll have fringe cases where your cards are helping other cards that aren't obvious but with the main point of them all benefiting Mellunite cards what is the reason for using a convoluted ability rather than simply reusing creature types?
Also, why would this only work in constructed? Unless you mean to invoke the 4 of rule for any cards named Mellunite in which case I can't imagine a good use of this mechanic at all.
There wasn't really a specific god for Temple of Abandon. Though Kruphix mentions that numerous gods have faded from memory and its been thoerized that the god of love mentioned should have been the RG god.
They've said they aren't doing the can't be in graveyard thing anymore, instead they aren't printing new 'good' reanimation and they have a ban list for problems that arise. Also I think that would fine without the 5
Can you tell me where WotC has said this? I'd be curious to read about it.
As with most things, our only source is Maro and while a lot of things are just his opinion he has said development made this call.
I think this came up in a column at some point but I can't find it easily, because I don't remember whose.
Edit: Found where it was mentioned in a column, and it was Maro again.
Ulamog, the Ceaseless Hunger
An interesting question I've gotten about Ulamog is why his original card in Rise of the Eldrazi had an anti-reanimation rider while the new version does not. The big answer is we've made a conscious choice to put the responsibility of reanimating giant creatures not on each giant creature but rather on the reanimation spells. That's why we've made them more expensive and moved them up in rarity. This felt like a better plan than having to add an extra clause onto every big creature.
I'm not sure if it is intuitive that Ila, Visionary Clairvoyant only makes you draw 1 card no matter how large of a scry they are replacing. Also it shuts down 'if you scry' abilities like Knowledge and Power, while this isn't a problem, having counter intuitive effects that you would want in the same deck should be avoided.
Heart of the Maelstrom 5WWUUBBRRGG
Legendary Creature- Elemental (M) 21/21
This probably needs the "this can't be in a graveyard" clause though.
They've said they aren't doing the can't be in graveyard thing anymore, instead they aren't printing new 'good' reanimation and they have a ban list for problems that arise. Also I think that would fine without the 5
The first thing is I can't imagine that a mythic vanilla isn't legendary, after that I'm stumped. It could be any combination of colors but 5 'feels' more mythic but considering we have Fusion Elemental what would push this to mythic? Possibly a strictly better Isamaru, Hound of Konda so 3/3 or 4/2?
Worldbend doesn't work the way you may think it does. With the way its worded you choose the player and permanent, then you get up to three un/tap choices depending on what is exiled. It seems you want this to un/tap up to three permanents if this is what you intended the easiest way is to drop the targeting on the permanents otherwise the wording will get very cluttered.
Other than that I would like to echo everything alwaysatoad said, very interesting designs and they pointed out the majority of the problems.
Reynol, Master Magus is interesting and annoying as all hell. His ability should be 'When you cast' not 'If you cast' look at the Eldrazi to see non conditional cast triggers.
Rez, Explorer of Realms's +1 may be fine putting the land into play. It is conditional card advantage but it only gets lands so into play should still be safe. Maybe into play tapped. That -2 isn't very strong even if the + is putting lands into your hand, certainly getting 2 Summer Blooms for 3 mana is insane but it happens over 3 turns so its rather underwhelming and requires other cards putting extra lands into your hand to really function. The ultimate seems disconnected from the other abilities. It still references lands but only as the modifier on its +/+, it might be better if this animated your lands or in someway made your lands better.
For the whole constructed vs limited, your idea is almost exactly tribal. It isn't hard to push tribal up to the numbers needed to be relevant in limited, look at Tarkir. There was a Semi-meaningful warrior tribal element to limited without saturating the set with warriors and that was without it even being a theme or mechanic of the set.
Also, why would this only work in constructed? Unless you mean to invoke the 4 of rule for any cards named Mellunite in which case I can't imagine a good use of this mechanic at all.
I think this came up in a column at some point but I can't find it easily, because I don't remember whose.
Edit: Found where it was mentioned in a column, and it was Maro again.