Do units heal at the end of non-combat showdowns? And is challenge considered spell damage?

To answer your questions:

1. Do units heal at the end of non-combat showdowns?

No. Units do not heal after a non-combat showdown.

According to RiftJudge FAQ #9726 and FAQ #9016, healing in Riftbound only occurs at two specific times:

• During a Combat Cleanup: This step only occurs after a combat showdown (a showdown contested by units controlled by different players).
• At the end of each player's turn: This occurs during the End of Turn Cleanup.

Since a non-combat showdown does not meet the definition of "combat," it does not trigger the Combat Cleanup healing process.

2. Is Challenge considered spell damage?

No. Challenge is not considered spell damage.

According to Rule 417.6.b.3, when a spell like Challenge is used, the damage is dealt by the chosen units, not by the Challenge spell itself.

• Rule 417.6.b.3: "When a spell or ability specifies a Unit as the source of the Damage for the Deal action, it is not in addition to the spell or ability that specified it. Example: Challenge is a spell that reads 'Choose a friendly unit and an enemy unit. They deal damage equal to their Mights to each other.' The damage that Challenge causes to be dealt is dealt by the chosen units, not by Challenge."

Because the units are the source of the damage, any effects that apply to "spell damage" (e.g., preventing damage from spells) would not apply to the damage dealt by Challenge.