I just want to verify how these two really interact in certain corner cases I've experienced recently, such as:
1) Player casts multiple creatures in same turn (let's say 3 creatures for this example), none of them have haste innately and no other boardwide haste effect is present either), all in same turn. Player has Lightning Greaves already out and equips it to each creature one at a time. Now player tries to attack with all these creatures saying they all have haste now due to Lightning Greaves being equipped to them.
My understanding is that all 3 creatures initially have summoning sickness, then have haste when and only while it is equipped with Greaves, thus when player moves Greaves to another creature, said creature loses haste and still suffers from summoning sickness.
3)Player A has Concordant Crossroads out. If he casts a creature then, before his combat step, someone destroys Concordant Crossroads , would said creature still have Summoning Sickness? same question can be applied appropriately to any other player casting a non-haste creature on their respective turn later on if this enchantment still exists at the time (no flash shenanigans)
1) Only the creature equipped with greaves would have haste. The others had haste while it was equipped but will no longer have it when it isn't. If they have 'summoning sickness' they will be unable to attack.
2 & 3) Each of those cards you listed have static abilities that only function while on the battlefield. While those cards are on the battlefield the creatures have haste, when they leave the battlefield they will no longer have haste. It's the same thing like honor of the pure , white creatures will only receive +1/+1 while it's on the battlefield, but will no longer have it if honor the pure leaves the battlefield.
The reason anger is worded the way it is, is because it has an ability the only functions while it's in the graveyard so it needs to specifically point out that the ability only works as long as its in the graveyard.
1) Player casts multiple creatures in same turn (let's say 3 creatures for this example), none of them have haste innately and no other boardwide haste effect is present either), all in same turn. Player has Lightning Greaves already out and equips it to each creature one at a time. Now player tries to attack with all these creatures saying they all have haste now due to Lightning Greaves being equipped to them.
My understanding is that all 3 creatures initially have summoning sickness, then have haste when and only while it is equipped with Greaves, thus when player moves Greaves to another creature, said creature loses haste and still suffers from summoning sickness.
Yes. A creature only has haste while it has haste. Lightning Greaves only applies haste while it's attached to a creature.
Same thing. Maelstrom Wanderer only applies haste while it's on the battlefield. Once it leaves, creatures no longer have haste.
3)Player A has Concordant Crossroads out. If he casts a creature then, before his combat step, someone destroys Concordant Crossroads , would said creature still have Summoning Sickness? same question can be applied appropriately to any other player casting a non-haste creature on their respective turn later on if this enchantment still exists at the time (no flash shenanigans)
Same thing. Crossroads' ability only applies while it's on the battlefield. Once it's gone, you no longer get its benefit.
How to autocard (do this to specify a card in your posts): Type [c]Black Lotus[/c] to get Black Lotus . Type [c=Black Lotus]The Overpowered One[/c] to get The Overpowered One .
508.1a. The active player chooses which creatures that he or she controls, if any, will attack. The chosen creatures must be untapped, and each one must either have haste or have been controlled by the active player continuously since the turn began.
702.10. Haste
702.10a. Haste is a static ability.
702.10b. If a creature has haste, it can attack even if it hasn't been controlled by its controller continuously since his or her most recent turn began. (See rule 302.6.)
702.10c. If a creature has haste, its controller can activate its activated abilities whose cost includes the tap symbol or the untap symbol even if that creature hasn't been controlled by that player continuously since his or her most recent turn began. (See rule 302.6.)
and
604. Handling Static Abilities
604.1. Static abilities do something all the time rather than being activated or triggered. They are written as statements, and they're simply true.
604.2. Static abilities create continuous effects, some of which are prevention effects or replacement effects. These effects are active as long as the permanent with the ability remains on the battlefield and has the ability, or as long as the object with the ability remains in the appropriate zone, as described in rule 112.6.
Haste doesn't "cure" summoning sickness; it just allows the creature to ignore it. When a creature loses haste (for the reasons previously explained), it becomes subject to the summoning sickness affecting it.
Haste doesn't "cure" summoning sickness; it just allows the creature to ignore it. When a creature loses haste (for the reasons previously explained), it becomes subject to the summoning sickness affecting it.
And this is true because technically, summoning sickness isn't something creatures "have" in the first place; it isn't a thing they can "lose". The relevant rule simply says that a creature (that doesn't have Haste) can't attack or use or abilities unless it's been under the same player's control continuously since the beginning of his or her most recent (possibly current) turn. There's nothing there about imposing a status like being tapped, or a videogame-style "condition". Haste lets creatures ignore this rule, but it's a mistake to think it "cures" or "removes" summoning sickness precisely because there's nothing to "cure" or "remove".
Jeff Heikkinen DCI Rules Advisor since Dec 25, 2011
or 
abilities unless it's been under the same player's control continuously since the beginning of his or her most recent (possibly current) turn. There's nothing there about imposing a status like being tapped, or a videogame-style "condition". Haste lets creatures ignore this rule, but it's a mistake to think it "cures" or "removes" summoning sickness precisely because there's nothing to "cure" or "remove".
