I think we can argue that it is a text-changing ability when we are replacing all of the text with another pre-defined text.
Target creature loses all abilities and gains flying, replaces all of the text but isn't a text changing ability.
As for confusing replacing each spell ability with draw a card. That does warrant some thought. Though, is it a problem to replace each spell ability with draw a card? I'm certain it can be taken advantage of but I doubt it's to such an extent that it's a problem in any format.
You are right in your thinking. The Witch specifically exempts creatures that can't attack for any reason while Festival makes it so no creatures can attack.
This is why learning how Wizards Templates their cards is important. There is no "Scrys" scry doesn't conjugate in that way. So the proper wording for your ability would be. "If a player would draw a card except the first one they draw in each of their draw steps, they scry 2 instead."
Also, don't use "Text" in the first card. This isn't a text-changing ability, it's an ability-changing ability. You reference Text when you are specifically altering a part of the text. When changing abilities wholesale you don't mention text.
Nueral Necklace. The phrase your looking for is Spell Abilities. You may replace the spell abilities of instant's and Sorcery's you cast with "Draw a card."
Nueral Decay, one or more is not needed, just say a. "If a player" This is a white effect. Though it's weak as white can just completely stop the draw. But those weaker version can be cheaper. Maybe 1MV.
White is only allowed to ramp when it's playing catch-up a perpetual extra land drop with possibly the easiest condition imaginable isn't something white gets.
Colored ward costs isn't really a thing. It falls back on the problem of swinging wildly in power. The rest of the card is meh.
Idle Curiosity needs more. It's too much mana for too mundane an effect. The additions I imagine pushes it's complexity to rare but here's the idea. "Discard a card. Mill 1: Look at each players hand and the top card of every library. You may mill 1." It might be too busy of a card now.
Scion, my gut says too much for common but only a bit. Maybe lower toughness.
Gallery Show, I like this. It's seems fine on power level but I'd make it easier to cast by not limiting it to a single graveyard for all the creatures
Why is this milling? It's extra text that is just confusing.
It's milling because it's replacing the lands being destroyed, exiled, sacrificed, or bounced simultaneously via Mass Land Removal spells such as Armageddon, Decree of Annihilation (without paying Cycling cost), Cataclysm, and Sunder. Even If the lands leave the battlefield due to a state-based action then the lands get replaced with whatever you mill from the top of your library.
Either you aren't using the word replacing in Magicese or your entire ability is improperly worded. Regardless, that doesn't answer why it's milling. Functionally, what gain is there to milling as opposed to simply putting the top card onto the battlefield?
Whenever a land leaves the battlefield, it's controller mills a card and puts it face-down on
the battlefield as a land with, "Tap, Add one mana of any color in your commander's color identity".
Treat the face-down land as though it were a basic land while on the battlefield. Players can look at
the bottom of the face-down cards at any time.
Whenever a land leaves the battlefield, it's controller puts the top card of their library face-down on
the battlefield as a land with, "Tap, Add one mana of any color in your commander's color identity".
Treat the face-down land as though it were a basic land while on the battlefield. Players can look at
the bottom of the face-down cards at any time.
There is a marginal amount of space saved by use of fewer words but why mechanically is this milling? Why have the added step of the top card hitting the graveyard? Its excess mechanical baggage that doesn't seem to serve the design at all.
Why is this milling? It's extra text that is just confusing. Spelling out your intent helps but this doesn't really do that. Mill doesn't want to waste time untapping and color fixing the opponent's lands. It could be amusing chaining together multiple destroy all lands cards. However, its main value is turning fecthlands and Ghostquarter and similar effects into ramp. WHile also empowering any land with a sacrifice ability. Probably broken beyond fixing.
Copies of the MirageRaptor will simply be polyraptors. The Mirage Mirror doesn't remember that it's a mirror when it changes so it doesn't copy that fact over to clones.
No, Hofri requires a nontoken creature to die. Meaning go from the battlefield to the graveyard. This doesn't happen with Leyline of the Void in play. The leyline is a replacement effect while Hofri is a trigger.
If a 9/9 with doublestrike is blocked or blocking a 6/5 with deathtouch. The 6/5 will die in firststrike damage step. So it won't deal damage to the 9/9.
OK, thats a combo. But without haste or this being an instant I don't think its that big a deal. More than enough moving parts that it shouldn't be an oppressive combo.
As for confusing replacing each spell ability with draw a card. That does warrant some thought. Though, is it a problem to replace each spell ability with draw a card? I'm certain it can be taken advantage of but I doubt it's to such an extent that it's a problem in any format.
Also, don't use "Text" in the first card. This isn't a text-changing ability, it's an ability-changing ability. You reference Text when you are specifically altering a part of the text. When changing abilities wholesale you don't mention text.
Nueral Decay, one or more is not needed, just say a. "If a player" This is a white effect. Though it's weak as white can just completely stop the draw. But those weaker version can be cheaper. Maybe 1MV.
Colored ward costs isn't really a thing. It falls back on the problem of swinging wildly in power. The rest of the card is meh.
Scion, my gut says too much for common but only a bit. Maybe lower toughness.
Gallery Show, I like this. It's seems fine on power level but I'd make it easier to cast by not limiting it to a single graveyard for all the creatures
Whenever a land leaves the battlefield, it's controller mills a card and puts it face-down on
the battlefield as a land with, "Tap, Add one mana of any color in your commander's color identity".
Treat the face-down land as though it were a basic land while on the battlefield. Players can look at
the bottom of the face-down cards at any time.
Whenever a land leaves the battlefield, it's controller puts the top card of their library face-down on
the battlefield as a land with, "Tap, Add one mana of any color in your commander's color identity".
Treat the face-down land as though it were a basic land while on the battlefield. Players can look at
the bottom of the face-down cards at any time.
There is a marginal amount of space saved by use of fewer words but why mechanically is this milling? Why have the added step of the top card hitting the graveyard? Its excess mechanical baggage that doesn't seem to serve the design at all.
Polyraptor
Copies of the MirageRaptor will simply be polyraptors. The Mirage Mirror doesn't remember that it's a mirror when it changes so it doesn't copy that fact over to clones.