Correct

Barney did this to my Kefnet with a festering mummy and a Grasp in a king of the hill match. This is what he is referring to, he just didn't specifically say reduce toughness to 0. I sent him a PM about it " I was like "aw s***" game 1 when you grasped my Kefnet by his bird balls."

Here's a paper magic question. Suppose my opponent has three Mountains. He plays another Mountain, Koth of the Hammer, uses the +1, and attempts to hit me for four. The problem: he used the +1 on the Mountain he just played. Since Koth does not give haste, the Mountain can't actually attack. If I call a judge, what will the judge say? I get that it's a "dick move" and I would probably not do it in real life unless it's something like a PT top 8, but still. Will the judge force my opponent to accept the mistake? Repair the situation? Issue me a warning for being a jerk?

It really depends on the Rules Enforcement Level (REL) of the event you're in. In a casual event the judge would probably explain to the new player what he did wrong and then allow them to change the decision on what mountain to target. If it continues to happen, as in it seems the new player either doesn't care to learn or thinks he can continue to get away with it then they might enforce the rule and make them accept that the creature couldn't attack.

At a competitive tournament the judge would just explain to the offending player what happened, and that his mountain has summoning sickness and then have the game continue, with an un-hasted 4/4 until EoT.

You should never get a warning about bringing up a rules question to a judge. Even if you do it in the guise of educating your opponent. Some players don't want to get into a confrontation so they won't explain rules to the opponent, and instead have a judge do it. The offending player is more likely to be receptive to constructive criticism from a judge than they would be by an opponent that they perceive as someone who's trying to get one in on them.

If you're just playing games with your friend, I would explain what he did wrong, allow him to take it back and attack me. Then I'd allow him that one more time. If my friend can't figure out what he's doing wrong after that then I'd start enforcing the rule. If he still can't figure it out, maybe magic isn't the game for them.

Another paper magic question. Suppose my opponent casts Supreme Verdict. I attempt to counter it with Warping Wail. Obviously, Supreme Verdict can't be countered, so:

Does the Warping Wail attempt to counter anyway (with no effect)?
Does the Warping Wail fizzle because there's no legal target?
Can I say "counter target sorcery" and then, upon realizing that Verdict can't be countered, choose one of the other modes for Warping Wail?

Well the last part more depends on the leniency of the playing group/judges. Normally it tries to counter and then just fizzles since the ability doesn't prevent it from being targeted in the first place.

If you realised it won't work before resolving things then its down to your playing environment and if the other player and/or judge is generous enough to let you take it back, though in a proper tournament it is more likely to be no I would imagine.

On a bit of a side note: If it did all the things instead of making you choose then the other two options would still happen despite the counter fizzling. However that is not the case and you have to choose one of the options when you're casting it so it only does that one option.

Thanks for answer. Does that mean if I use Cryptic Command to draw a card & bounce your Scaled Behemoth, the play would be illegal and I can therefore choose one of the other modes on the Command, but I cannot decide not to play Cryptic Command? What if I had cast a card like Murder targeting the Behemoth instead, and there are no other legal targets?

I vaguely recall that if I use Cryptic to bounce e.g. Mogg Fanatic and draw a card, you can sacrifice Mogg Fanatic to itself and the Cryptic would fizzle, too.

Not sure on the first part but for the second a spell needs a valid target, otherwise it fizzles so if you sacrifice the fanatic the spell won't resolve (but say cryptic command read "target player draws a card" then even if the mogg was sacrificed you'd still draw a card as their was still 1 valid target)

For the first part - you don't. You cannot put cryptic command on the stack with an illegal target. That action would never happen. It is a very different example compared to your earlier question
This also means that you cannot play Murder if there are no legal targets. Playing a spell means you declare any targets and choices, then put it on the stack. If you have no other plays, you pass priority and your opponent can respond with instant effects. If your opponent has no plays or chooses not to do anything, he/she pass priority back and the spell resolves. When resolving, all targets are checked again and if all targets of a spell has become illegal, the spell "fizzles". "Fizzle" is a very old wording, for the past 10 or so years, it has been replaced with "countered due to all legal targets have become illegal" or some such. It's still used as a casual term meaning the same thing.

From the comprehensive rules:

608.2b If the spell or ability specifies targets, it checks whether the targets are still legal. A target that’s no longer in the zone it was in when it was targeted is illegal. Other changes to the game state may cause a target to no longer be legal; for example, its characteristics may have changed or an effect may have changed the text of the spell. If the source of an ability has left the zone it was in, its last known information is used during this process. The spell or ability is countered if all its targets, for every instance of the word “target,” are now illegal. If the spell or ability is not countered, it will resolve normally. Illegal targets, if any, won’t be affected by parts of a resolving spell’s effect for which they’re illegal. Other parts of the effect for which those targets are not illegal may still affect them. If the spell or ability creates any continuous effects that affect game rules (see rule 613.10), those effects don’t apply to illegal targets. If part of the effect requires information about an illegal target, it fails to determine any such information. Any part of the effect that requires that information won’t happen.

The second part was already answered by Nighthawk.

So basically if I attempt to Cryptic Command your Scaled Behemoth, what actually happens is that I can't cast it -> it returns to my hand and I untap my lands?

in a nutshell, yes

Can a 0 power creature be tapped by a vehicle along with other creatures that add up to the crew cost?

For example 3 1/1 servos and a 0/1 Weaponcraft Enthusiast all tapping to activate Heart of Kiran or Thing in the ice 0/4 and a 1/1 thopter to activate Aethersphere Harvester.

Have a friend that disagreed with me on how this should work. Wondering if anyone has a definitive answer as I am not sure.

For anyone curious as to why anyone would want to do this... throne of the god-pharaoh

Sure you can.

Sadly my efforts on duels will only allow me to tap the 1 power creature and removes the 0 power creature.

??? Is that a platform specific problem? On iOS that's not an issue; you can tap all the additional creatures you want so long as you meet the requirement, you just can't have a partial crew. You can also re-crew an already crewed vehicle but you have to meet the full requirement each time. So you can't crew Skysovereign with 3 servos and add a weaponcraft enthusiast on its own later; you'd either have to do them all at once or find another 3 power and add the enthusiast to that.

Note that your activated vehicles can even crew themselves, which can help milk extra damage out of the Throne with Heart of Kiran or anything with summoning sickness.

What happens if my opponent has Leyline of Sanctity in play and I attempt to tap Forbidden Orchard for mana?

I'm guessing I can't tap Forbidden Orchard, but it is a mana ability, so just checking.

I don't see why you couldn't tap Forbidden Orchard. The Hexproof from Leyline only prevents you from being the target of your opponents' spells and abilities, not your own.

Right but the text on Forbidden Orchard says "target opponent".

EDIT: actually now I think I can tap Forbidden Orchard? The text on it doesn't say [T], target opponent creates a 1/1 colorless spirit token: add one mana of any color to your mana pool. In other words, the "create token" ability is a triggered one not part of the cost, and that's stopped by hexproof, i.e. this is a case in which my opponent having Leyline actually helps me (if I'm not playing Oath of Druids anyway). On the other hand if the wording had said that it's part of the cost then I can't tap it for mana (?).

Yeah, I misread your original question, but I'm going to act as if that's your fault, anyway. Come on, Banedon. Why you gotta be like that?

Correct.