Omophagea: how does this even work. Do they gain Knowledge (Devoured Enemy)?

Whenever it says "may reroll a given characteristic" for any failed test, does this just mean they are totally incapable of failing said test? I.e. because of Mucranoid they are never able to fail temperature tests? Is it a reroll any one time?

An unrelated aside: can they trigger both chapter and personal demeanor once per game session, or just one demeanor per session?

The way I perceive the Omophagea to work and how I use it is that once they devour a chunk of the opponent (assuming they dont suffer ill effects from their light snack) is that the GM grants them a piece of potentially plot useful information which the victim would know. I tend not to go down the whole "give them skills temporarily" route. It's basically a quick way of getting intel.

Regarding the mucranoid, incorrect. A character is capable of failing a test. The rule of rerolls states that any circumstance where you are allowed to retake a test, the second result stands irrespective of whether it is better/worse than the previous result. Any and all tests can be failed if the character rolls in that dreaded upper block of numbers. For my lot we say the threshold of critical failure is 96 - 00 however some parts go with 91 - 00. Some GMs then go on to say that any result in this critical failure range result in particularly painful or humorous side effects. If the character rolls this then irrespective of any and all modifiers or skill area the test fails but they can still try to reroll if applicable. Additionally you are not allowed to reroll a reroll by any method whatsoever:

Eg: Mucranoid to retake the toughness test you failed, you cannot then use a fate point to reroll it again. You must take the second result.

You must also take into account that there are a few times (can't recall any off top of head) when a character must retake a test and times where they may choose to retake a test. As above remember that the second result stands for better or worse and there may be times you may want to take the normal failure on the first test rather than risk a second try and get more degrees of failure or worse, critical failure.

Omophagea: how does this even work. Do they gain Knowledge (Devoured Enemy)?

Whenever it says "may reroll a given characteristic" for any failed test, does this just mean they are totally incapable of failing said test? I.e. because of Mucranoid they are never able to fail temperature tests? Is it a reroll any one time?

The omophagea was originally meant to teach space marines instinctual or common memories of the creatures they eat in their operating theatres. They would hunt, then eat, some of the toughest creatures wherever they go and by doing so they would begin learning the instinctual and environmental knowledge of the location. Where water is, what is safe (for the eaten creature) to eat, good places to rest and sleep at night, etc. Even if you accept they can gain different kind of memories, they should not be capable of learning specific information. The location (direction to and familiar surroundings) of their home base they have been based out of for years - yes. The specific coordinates of a new forward oporating base the victim only just learned about - no. Definately not skills (although if the demo-trooper has worked with a certain explosive for years the Astartes may be able to learn how to disarm or detonate these commonly used explosives).

Any re-roll is a one time thing. You do not get to continue re-rolling until you succeed, just once and if your second roll is a fail you still fail.

An unrelated aside: can they trigger both chapter and personal demeanor once per game session, or just one demeanor per session?

"Demeanour may be triggered a maximum of once ( and only once, no matter how many demeanours he may have !) per game session." Page 33 Deathewatch Core Rulebook.

Thanks everyone. GMing DW with a crowd of six equally new DW players is made quite a lot simpler with all of you answering questions.

Omophagea: how does this even work. Do they gain Knowledge (Devoured Enemy)?

Whenever it says "may reroll a given characteristic" for any failed test, does this just mean they are totally incapable of failing said test? I.e. because of Mucranoid they are never able to fail temperature tests? Is it a reroll any one time?

The omophagea was originally meant to teach space marines instinctual or common memories of the creatures they eat in their operating theatres. They would hunt, then eat, some of the toughest creatures wherever they go and by doing so they would begin learning the instinctual and environmental knowledge of the location. Where water is, what is safe (for the eaten creature) to eat, good places to rest and sleep at night, etc. Even if you accept they can gain different kind of memories, they should not be capable of learning specific information. The location (direction to and familiar surroundings) of their home base they have been based out of for years - yes. The specific coordinates of a new forward oporating base the victim only just learned about - no. Definately not skills (although if the demo-trooper has worked with a certain explosive for years the Astartes may be able to learn how to disarm or detonate these commonly used explosives).

Any re-roll is a one time thing. You do not get to continue re-rolling until you succeed, just once and if your second roll is a fail you still fail.

An unrelated aside: can they trigger both chapter and personal demeanor once per game session, or just one demeanor per session?

"Demeanour may be triggered a maximum of once ( and only once, no matter how many demeanours he may have !) per game session." Page 33 Deathewatch Core Rulebook.

Herichimo, I think you've commented on everything I've posted, lol. So thanks for that.