Paying X=0 with cost reduction effects
Asked by legendofa 1 year ago
I have Umori, the Collector and Rayami, First of the Fallen out and Stonecoil Serpent in hand. I want to have Stonecoil Serpent enter the battlefield with toughness 0, so it does and gets exiled with Rayami's blood counter. Is the Serpent forced to enter with a +1/+1 counter if I cast if for X=0? Is it possible to cast Serpent with X=(-1)?
If you cast Stonecoil Serpent with X=0 it will enter with 0 +1/+1 counters (unless another effect like Renata, Called to the Hunt makes it enter with a counter). Even though Umori, the Collector lets you pay when you choose x=1, it does not prevent you from choosing x=0. You cannot choose a value less than 0 for X.
August 17, 2022 12:04 p.m.
To go in depth on Neotrup's answer, you declare the value for X before paying any costs.
If you look at the steps of casting a spell (Which comprises rules 601.2a - 601.2i), the second step (601.2b) is a wall of text, so I'll pull a small synopsis from the middle:
"...If the spell has a variable cost that will be paid as it’s being cast (such as an {X} in its mana cost; see rule 107.3), the player announces the value of that variable..."
You've declared a value for X. Now we skip past rules 601.2c-601.2e as they involve targets, distribution of values, and legality (Which aren't relevant here). 601.2f leads into the next part (Bolded parts are relevant):
"The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative costs. Some effects may increase or reduce the cost to pay, or may provide other alternative costs. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost or alternative cost (as determined in rule 601.2b), plus all additional costs and cost increases, and minus all cost reductions" If multiple cost reductions apply, the player may apply them in any order. If the mana component of the total cost is reduced to nothing by cost reduction effects, it is considered to be {0}. It can’t be reduced to less than {0}..."
You take the value you declared for X (0), add additional costs (None here, so still costs 0), and subtract cost reductions (Since spells can't cost less than 0 mana it'll still costs 0).
At this point you run through the rest of the casting process, and the Serpent will ultimately enter with 0 counters, where it'll die, be exiled, and give Rayami some abilities
legendofa says... #1
...enter the battlefield with toughness 0, so it dies and gets exiled...
(editing)
August 17, 2022 11:29 a.m.