magic the gathering rules?

There's a few technical issues in the previous answers that need to be clarified:

First, you play Lawbringer's ability, which as part of the cost to play the ability, you sacrifice Lawbringer. In order to play the ability, you have to have a legal target. Since the red creature has shroud, due to Whispersilk Cloak and Lawbringer isn't a red creature, then you can't play the ability at all. Which means, you can't even sacrifice Lawbringer. Without being able to play Lawbringer's ability, you can't ever pay the cost.

This is important to note, as you don't just sacrifice Lawbringer to get an "effect". You sacrifice Lawbringer as part of playing its ability. Think of it like buying a bus ticket. If you can't buy the bus ticket because the window is closed, you don't just throw your cash/credit card at the window. You only use your cash/credit card if you can actually buy the ticket. The same is true with Lawbringer. You have to be able to play the ability first. If you can't, then you aren't able to pay the cost of sacrificing Lawbringer. This is the point that Steve is technically incorrect on.

Second, Lawbringer's ability is just that, an activated ability that you can play. When it resolves, it has a one-shot effect of destroying the targeted red creature. Effects are usually part of the resolution of a spell or ability. So, you don't "get" an effect by sacrificing Lawbringer. You play its ability, sacrifice Lawbringer, and then the effect happens when the ability resolves. Hence why you can respond to spells or abilities: the effect doesn't happen until resolution, and you can play your own spells and abilities in response, before that happens.

To break it down: Giving the red creature shroud before Lawbringer's ability can be played, means that it's not a legal target for Lawbringer's ability and the ability can't be played. Giving the red creature shroud in response to Lawbringer's ability would cause the ability to be countered on resolution. Using Lawbringer's ability in response to the equip ability of Whispersilk Cloak (or something else that gave it shroud), would mean Lawbringer's ability resolves first (since it was played most recently) and the red creature is destroyed before it ever actually gains shroud.

Anything a creature has on it is an ability. Since his creature has whispersilk cloak on it you can't target it with the lawbringer since you have no creature to target. You answered your own question anyways if you re-read it. The tap/sacrifice part is what the ability so you can use it until you get rid of whispersilk cloak.

Shroud makes the creature untargetable, albeit be spell or ability. If you sac the lawbringer, you need a valid target or the ability dissipates. A shrouded creature is not a valid target. Now if you want to play cruel edict or barter in blood, that is a different story.

If the creature is already cloaked, the shroud will prevent it from being targeted. So you have to remove the cloak before you can kill the creature. If you sacrificed to kill the creature, the effect will sizzle and you will lose your creature and his will be standing tall.

If you sacrificed while he is attempting to cloak the creature, then you will have successfully removed it from the game since equip is at sorcery speed and remove is at instant speed.

The formation of a species means that a group of organisms splits into two populations that cannot reproduce with one another. The reigning model of reproductive isolation holds that genetic differences accumulate between populations that render their hybrid offspring dead or sterile, like the mule, an infertile child of the donkey and horse. Many researchers have long assumed that this isolation must be the result of changes in gene sequence that introduce an incompatibility between groups, such as new sperm that do not recognize the old eggs. But examples of such speciation genes are very few.

editit- yup makes sense guess i was wrong dci judge is right hmmm!!!! So you cannot sac the lawbringer unless you have a legimite target ok

auto-effect from the ability

Be careful because it might kill.