If you've been keeping up with our FAQs, you'll know that spells resolve from left to right, but what you might not realize is that spells aren't the only ones paying attention to direction. It's time to talk about order resolution.
Like we mentioned before, most things in Runeterra go left to right. Your left-most unit attacks first and the left-most Deny is the one that matters.
However, in the event that a spell or effect could target multiple cards with the same parameters, there are mechanics in place to handle how these spells and effects get resolved. For example, a unit that targets the Weakest enemies first looks for the lowest power unit, then the lowest health. If those parameters are tied, it will look for the unit with the lowest cost. If a tie cannot be resolved in this way, units will be targeted in from left to right. This is the Tiebreaker Rule.
Sometimes who deals what damage to where can get confusing. If you're ever unsure where the hurt will land, remember to make the Oracle's Eye your bff, so you'll never wonder what damage is going where.
In Your Hand
Now that we've got all the basics out of the way, let's see how this plays out in your hand:
Let's pretend this is your current hand (Zed being on the left) and Arena Bookie is on your board. At the start of a new round, Arena Bookie's ability causes your lowest cost card to be discarded. Since both Zed and Shadowshift cost 3 mana each, and the only parameter here is lowest cost, there's now a tie between Zed and Shadowshift! As a result, Zed gets discarded.
Be sure to look at the order of your cards before playing a unit or spell that could get rid of something you'd rather hold onto.
On the Board
Now how's about we take a look at how this could play out on the board:
Your eyes have not deceived you! In our attempt to startle you into surrender, we have summoned not one, but three Poros to defend our Nexus! They even managed to hold the line when your Ephemeral unit died this round. What will you do now?
Being the intrepid deck buster that you are, you respond with Rhasa the Sunderer. Oh... Their ability takes out two of my weakest units... Since the power, health, AND cost are the same between my poor Poros, the order of operations proves the tiebreaker once more. I must bid farewell to my Sinister and Daring Poros (since they're the ones on the left). At least you left me with the Affectionate one.