I know that the general ruling is that cards add their traits to a check when they are used. (But their are exception like the Crown of Charisma of i recall correctly)
So a Warhamer would be a strength or melee attack with the melee trait and bludgeoning trait. Now if someone would play a longbow+1 to help, does the check have the melee, ranged, bludgeoning, piercing and magic trait?
2 little example to clarify:
Kyra encounters an Ancient Skeleton and has a Mace in her hand.
She reveals it for her combat check and Valeros decide to help her by discarding (recharging with his power) a longbow.
So, if the longbow adds his traits, Valeros "helped" Kyra by giving her a d4 and increasing the difficulty of the combat check by 3.
Example 2: Kyra encounters an Shadow and has a Mace in her hand.
She reveals it for her combat check and Valeros decide to help her by discarding (recharging with his power) a longbow+1.
So, if the longbow+1 adds his traits, Valeros helped Kyra by giving her a d4+1 and more importantly the magic trait.
From my understanding, if a player discards a card to add a die to a check, that's all they're doing: adding a die. None of the traits are added.
In your 2 examples Kyra would be adding traits from her cards, but Valeros is not adding any traits and is helping Kyra out with an additional 1d4 to her checks.
The attempting a check sequence is the following.
- Attempting A Check
- Determine which die you’re using.
- Determine the difficulty.
- Play cards and use powers that affect the check (optional).
- Assemble your dice.
- Attempt the roll.
- Take damage if you lose a check against a monster.
The ruling is that only cards played during the "Determine Which Die You're Using" step add their traits. That step says this in the rulebook:
Determine Which Die You’re Using... Some cards may allow you to replace the required skill for a check with a different one; as part of this action, you may play only 1 card or use only 1 power that changes the skill you are going to use. When you play a card that does this, add that card’s traits to the check; for example, revealing the weapon Longsword +1 for your combat check adds the Sword, Melee, Slashing, and Magic traits to the check.
Things like the Crown of Charisma are played during the "Play cards and use powers that affect the check" step, not during the "determine the die you're using" step. Hence the Crown doesn't add its traits. A weapon played by the character attempting the check though does get played in the "determine the die" step, so it would add its traits.
Play Cards and Use Powers That Affect the Check (Optional). Players may now play cards or use powers that affect the check. Players may not play cards that modify a skill unless you’re using that skill, and players may not play cards that affect combat unless you’re attempting a combat check. Do not add traits from these cards to the check; for example, playing the spell Guidance on a check does not give the check the Divine trait.
So other characters play their cards during the "that affect the check" step, so they don't add their traits. So Valeros in your examples can't give the check the piercing or magic traits. But he can still give the checks the extra dice.
The exception would be any card that said to add a trait. The Spiny Shield for example says to add 1d4 and the Ranged and Magic traits to your check, even though you are playing it in the "affect the check" step.