Drought Recovery doesn't work, all face down cards are 2/2 colorless vanilla creatures, the rules probably can't handle multiple definitions of what that means.
Trade Agreement, the Face-up on the exile is unnecessary, cards are always exiled face-up unless explicitly stated otherwise. The wording functions as is but there is an awkward function that you may not want. When you cast the first spell, the ability to return them triggers, but you will be able to cast any instants left over before they get returned by responding to the trigger. If this is ok then the card is fine.
Characteristic-defining ability are well defined within the rules so technically you can remove all noncharacteristic-defining abilities. It might confuse players but the rules can handle it well enough.
These types of questions are normally asked in the Custom Card Ruling subforum of the Custom Card forum in Creativity. The normal magic rules area is for actual cards and abilities, though I don't know if its actually against the rules to post your questions here.
It's really hard to say where you want them on the power scale, but when they compare unfavorably to unfavored existing cards then something should change. This is actually a big problem with fetchland variants, there aren't a lot of options to make them feel different without just being strictly better or worse than existing versions.
What about a bounce land version? Sac it and another land to get two lands?
For your double discard varient, based on the wording I assume you meant to grab two lands, but is it one of each or just two in a combination? Of your etbt variations this is the only one likely to see play due to the fixing of mana screw.
The rare Evolving Wilds is essentially fetching a shock land except you don't have both colors
Trifetch honestly seems worse than the panoramas. High life payment, etbt, and opp draws that is harsh.
Card Disadvantage Variant, this is also seems worse than its currently existing version, the slow fetches. Mountain Valley
Madness/Reanimator Variant looks like the best one. Specific decks will love the easy access to discard, so their isn't a downside.
Regenerate functions as a shield. It must be activated or granted preemptively, then it stays until the end of turn.
Regenerate replaces the act of destruction with the act of tapping the creature, removing it from combat, and removing all damage from it. Destruction is only the result of lethal damage (damage marked on the creature equal to or exceeding it's toughness) and effects that explicitly say destroy. Sacrifice, having 0 or less toughness and exile are not destroy effects.
Why the ph=f thing? It actually makes it a lot harder to go through what you said.
I wouldn't call what your doing 'fixing' phasing as you are actually leaving it mostly alone but adding an extra rule, so its more expanding than fixing. You start by explaining why phasing isn't used, the whole problem of understanding, but then kind of ignore this as though it isn't and was never an actual problem. So why bring it up? It is was a problem then it is still a problem that your tweak doesn't address. Other than that I would enjoy this change to phasing and its reintroduction, but it seems incredibly unlikely due to the reason you pointed out.
Gameplay-focused Commander player here. I like O-Kagachi as a card. Ludevic was just kinda weird and bad. I've wanted WRB Agrus Kos (Guildpact) and WUR Agrus Kos ghost (Dissension) for over 10 years.
Why are you adding extra colors to Kos? Especially black? He got an acceptable card showing off his unremarkable leadership skills. So it hardly seems reasonable to hope for more cards for him when so many still lack cards.
Yes, you preform the actions of a card in the order they are written. So first you create X Zombies, the the game counts the number of zombies you control to give the targeted creature -1/-1 for each one.
If you want it to be similar to reds impulse draw then it has to be random, anything else either is out of reds pie or significantly over powered. While normally random doesn't equal red it can be use to justify stretches(not breaks), and getting any card from the grave is a stretch for red.
Is there anything wrong with the way its been done before(Mizzix's Mastery, Past in Flames) ? Because if the main problem you are trying to fix is powerlevel your going to be running into a lot of problems. If you want something that can be done more often or regularly you want a toned down version, not cranked to 11. Non overload Mastery for 3 is probably the starting point.
State based actions are checked whenever a player would get priority(Such as passing between phases or after spells and abilities resolve) and when the turn ends.
That said State based actions have nothing to do with your question. The moment Bonescythe Sliver is off the battlefield its static ability no longer grants Double Strike. State based actions are what would send the Bonescythe to the graveyard after you bolt it(lethal damage is marked on a creature).
Flesh Graft doesn't work the way it's worded, to get the effect you desire you need to target both creatures regardless of what type of mana you plan on spending, this changes the card significantly because you need two targets to cast the spell so it can't strip the counters from a lone creature. The simplest fix is removed the targeting from the secondary portion of the spell. If you want to keep it target it needs new wording.
Thirst for blood, this effect feels very red, what's your reasoning for moving it to black? If you want to keep it you should move the sacrifice to end of Combat to make better use of your reap cards. Yes it works with reap as is but it's less obvious.
Unbury, Grim Discovery says you can get both. Also I assume you have a common fetchland in the set.
A more powerful past in flames, that fuels extra copies and goes infinite with just two and a few rituals? While the concept is interesting (it's essentially past in flames) the execution makes Yawgmoth's Will seem tame by comparison.
Doesn't the one that uses all the power go off turn 1? And if that's so far off, what turns do legacy/vintage usually win in?
Also the first 2 you mentioned didn't have parenthesis with their likelihood which would be half lol.
Yes, half of the ones I listed, which I stated weren't even half the Formats. So half of less than half and inconsistently at best(maybe worse?) doesn't come any where close to half.
Trade Agreement, the Face-up on the exile is unnecessary, cards are always exiled face-up unless explicitly stated otherwise. The wording functions as is but there is an awkward function that you may not want. When you cast the first spell, the ability to return them triggers, but you will be able to cast any instants left over before they get returned by responding to the trigger. If this is ok then the card is fine.
These types of questions are normally asked in the Custom Card Ruling subforum of the Custom Card forum in Creativity. The normal magic rules area is for actual cards and abilities, though I don't know if its actually against the rules to post your questions here.
What about a bounce land version? Sac it and another land to get two lands?
The rare Evolving Wilds is essentially fetching a shock land except you don't have both colors
Trifetch honestly seems worse than the panoramas. High life payment, etbt, and opp draws that is harsh.
Card Disadvantage Variant, this is also seems worse than its currently existing version, the slow fetches. Mountain Valley
Madness/Reanimator Variant looks like the best one. Specific decks will love the easy access to discard, so their isn't a downside.
Regenerate replaces the act of destruction with the act of tapping the creature, removing it from combat, and removing all damage from it. Destruction is only the result of lethal damage (damage marked on the creature equal to or exceeding it's toughness) and effects that explicitly say destroy. Sacrifice, having 0 or less toughness and exile are not destroy effects.
I wouldn't call what your doing 'fixing' phasing as you are actually leaving it mostly alone but adding an extra rule, so its more expanding than fixing. You start by explaining why phasing isn't used, the whole problem of understanding, but then kind of ignore this as though it isn't and was never an actual problem. So why bring it up? It is was a problem then it is still a problem that your tweak doesn't address. Other than that I would enjoy this change to phasing and its reintroduction, but it seems incredibly unlikely due to the reason you pointed out.
That said State based actions have nothing to do with your question. The moment Bonescythe Sliver is off the battlefield its static ability no longer grants Double Strike. State based actions are what would send the Bonescythe to the graveyard after you bolt it(lethal damage is marked on a creature).
Thirst for blood, this effect feels very red, what's your reasoning for moving it to black? If you want to keep it you should move the sacrifice to end of Combat to make better use of your reap cards. Yes it works with reap as is but it's less obvious.
Unbury, Grim Discovery says you can get both. Also I assume you have a common fetchland in the set.