I need some assistance with understanding how many +1/+1 counters Crystalline Crawler enters with. The board state is displayed in the screencap. Crawler is on the stack. Blue and green mana were spent to cast it. What is the maximum amount of counters I can put on this thing by optimally stacking my triggers?
Effects that add counters, such as found in Pir or Master Biomancer (another example is Winding Constrictor), include those that say "that many ... plus one ... are put on [it] instead" or "an additional ... counter" (C.R. 614.1a, 614.1c).
Effects that double counters, such as found in Doubling Season, include those that say "twice that many of those counters ... instead" (C.R. 614.1a).
To maximize the number of counters put on a permanent you control, apply applicable effects that would add counters to that permanent first, then apply applicable effects that would double (or multiply by more than two) counters on that permanent (C.R. 616.1). (Note that the replacement effects found in Pir, Master Biomancer, and Doubling Season are not from triggered abilities, since those abilities don't include "when", "at", or "whenever" [C.R. 603.1].)
Okay, so Crawler is entering with 2 from Converge, adding another 1 from Pir, therefore 3. Then we double it to 6? Next Biomancer gives 2, adding 1 from Pir, doubling that to 12? Is 12 the maximum?
Okay, so Crawler is entering with 2 from Converge, adding another 1 from Pir, therefore 3. Then we double it to 6? Next Biomancer gives 2, adding 1 from Pir, doubling that to 12? Is 12 the maximum?
Why are you doubling twice?
Crawler would enter with 2 counters. Pir adds one counter, so Crawler is going to enter with 3. Master Biomancer adds two more, so now Crawler is going to enter with 5. When Doubling Season doubles it, so Crawler ends up entering with 10.
No. Crawler would enter with 2 counters, Biomancer adds 2, Pir adds 1, then you double, for a total of (2+2+1)*2=10 counters. Each replacement effect only gets one chance to apply to any given event or modified event (exception being Commander with its command zone replacement rule, which can apply multiple times for the same event or modified event).
Okay, so Crawler is entering with 2 from Converge, adding another 1 from Pir, therefore 3. Then we double it to 6? Next Biomancer gives 2, adding 1 from Pir, doubling that to 12? Is 12 the maximum?
In general, a given replacement effect can apply only once to a given event "or any modified events that may replace that event" (C.R. 614.5). For example, if you control one Doubling Season, Doubling Season doubles (not quadruples or multiplies by some other number) the number of counters an effect would put on a permanent you control.
EDIT (Apr. 17, 2020): Change quoted text to conform to rule update with Ikoria: Lair of Behemoths.
Note also that, as implied by peteroupc's first comment, you choose what order to apply the replacements effects in. 10 is the maximum you can get in the situation, but you could potentially apply Doubling Season first, then apply Pir and Biomancer, for 2*2+2+1=7 counters. Under most circumstances you probably don't want that, but an opponent might Mindslaver you and force you to do it that way, for example.
Doubling Season
Master Biomancer
I need some assistance with understanding how many +1/+1 counters Crystalline Crawler enters with. The board state is displayed in the screencap. Crawler is on the stack. Blue and green mana were spent to cast it. What is the maximum amount of counters I can put on this thing by optimally stacking my triggers?
Effects that double counters, such as found in Doubling Season, include those that say "twice that many of those counters ... instead" (C.R. 614.1a).
To maximize the number of counters put on a permanent you control, apply applicable effects that would add counters to that permanent first, then apply applicable effects that would double (or multiply by more than two) counters on that permanent (C.R. 616.1). (Note that the replacement effects found in Pir, Master Biomancer, and Doubling Season are not from triggered abilities, since those abilities don't include "when", "at", or "whenever" [C.R. 603.1].)
EDIT (Oct. 11, 2019): Correctness edit.
Why are you doubling twice?
Crawler would enter with 2 counters. Pir adds one counter, so Crawler is going to enter with 3. Master Biomancer adds two more, so now Crawler is going to enter with 5. When Doubling Season doubles it, so Crawler ends up entering with 10.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
EDIT (Apr. 17, 2020): Change quoted text to conform to rule update with Ikoria: Lair of Behemoths.
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)