Common Confusion
Plaid Hat Games maintains a FAQ for Ashes Reborn, which can be found here. Other sources of confusion are listed below.
"Blocking" vs "Guarding" (Master set rules, page 10)
Blocking is when one or more of your units are intercept opposing unit(s) attacking your Phoenixborn.
Guarding is when either your Phoenixborn or a unit with the ability Unit Guard is put in front of an opposing unit attacking one of your units. Using your Phoenixborn to guard is usually referred to as "PB Guard" and can only be done once per round. When playing with physical cards, using the Phoenixborn Guard is represented by turning your PB sideways.
How/when fatigue works (Master set rules, page 6)
Fatigue damage occurs during the Prepare Phase (start of a round) when you have to draw until you have at least 5 cards in hand. For every card below 5 you are unable to draw, you take 1 damage on your PB;Phoenixborn; this is referred to as fatigue damage. For example, if you have 3 cards in hand, and only 1 card left in deck,your draw pile, you will take 1 fatigue damage that round. If you already have, or draw up to, at least 5 cards during the Prepare Phase, you will not take fatigue damage.
There are other cards and that can punish having an empty draw pile but these are not fatigue damage, and the damage effect is stated on the card. For an example of this, see Abundance.
When do units exhaust as part of combat resolution (Master set rules, page 10)
For attackers, exhaustion tokens are placed after resolving combatcombat, if their wounds do not exceed their life.
For blockers and unit guards, exhaustion tokens are placed as a result of countering an attack. The Alert ability (e.g. Hammer Knight) prevents exhaustion being placed as a result of countering. A guarding Phoenixborn does not get an exhaustion token.token; they are turned sideways to indicate that they have guarded this round.
It is possible due to the resolution of effects and abilities that a defender does not exhaust if the attacking unit they are blocking is removed from combat before countering occurs. One example is Crystal Archer's Preemptive Shot 1 which can destroy a 1-life attacker when the Archer is declared as a blocker.
Targeting specifics
Any card that says "target (something)" targets a card. Examples include "target unit," "target Phoenixborn," and, in the case of Whiplash (from the Corpse of Viros expansion), "target leftmost unit." Cards that have an effect that do not say "target," do not target (e.g. Nature's Wrath). Cards that target may be stopped by the appropriate card that cancels the effect (Golden Veil for units, Vanish for Phoenixborn or players).
Alterations target when they are attached, as per definition in the Master set rules, page 22.
"End of the round" (Master set rules, page 13)
Abilities and effects that trigger "at the end of the round," like Cursed 1 on Blood Puppet, happen after the Recovery phase, as per Master set rules on page 13.phase. These effects are outside of the Player Turns phase, which means Reaction cards and abilities cannot be played during this phase. However, abilities that trigger off of effects caused by any end of round abilities will still trigger.
Example: At the end of the round, a player using Jessa Na Ni has a Chant of Revenge and a Blood Archer with Fade Away attached. After the recovery phase, Fade Away triggers, destroying the Blood Archer and removing it from the game. Jessa cannot use Screams of the Departed because the ability states "Once per turn," and it is not during a turn. Chant of Revenge, however, gets a status token.
Reactions
You can only play reactions during the Player Turns phase; this means that the Prepare and Recovery phases do not allow for reactions or reaction abilities (blue text boxes, such as the one on Swift Messenger). As such, you are not allowed to use Summon Sleeping Widows or Final Cry as a reaction to a unit you control being destroyed at the end of the round due to an effect like Fade Away or the Fade ability.
There is a difference between Reaction spells and Reaction abilities, but only for cards that explicitly differentiate between them (Law of Sight). However, there is no difference between them in terms of Reactions per turn limit; if a player plays a Reaction ability in a turn, they are not allowed to play a Reaction spell later that same turn, or vice versa.
It is possible to play a Reaction to a Reaction. If a unit you control is destroyed by damage, and you respond with Summon Sleeping Widows, your opponent may then respond with Ice Trap to destroy one of the Sleeping Widows, provided they have not already played a Reaction this turn.
Area of Effect (AOE) Selection and Resolution (Master set rules, page 17)
Some abilities and spells are card "area of effect" spells, because they do not target (e.g. Mist Typhoon). When these spells and abilities resolve, only the cards currently in play may be affected. In some cases, the affected cards may change during the resolution process, however, their initial selection does not get undone; they are still affected by the ability or spell. These spells and abilities affect units with Concealed (such as Stormwind Sniper or The Corpse of Viros's Lurk aspect), as Concealed only protects from targeted spells and abilities.
Example of resolution: Survival of the Fittest is played, and one player controls a Gilder and a Blood Archer, neither with any tokens. If the player who played Survival selects the Gilder first, and places the status token from the Gilder's Inheritance 1 ability onto the Blood Archer, the Blood Archer is still destroyed as a part of the resolution of Survival of the Fittest, as it did not have a token when it was selected as an affected unit.
Coming soon
AOE selection and resolutionReaction windows (partially covered in "End of the round"- Specific card confusion
- Strange Copy
- Void Pulse and Return to Soil
- Rowan's Conscript ability