If I Bioshift 5 +1/+1 counters from Toothy, Imaginary Friend onto Fathom Mage with Pir, Imaginitive Rascal on the field, how many cards do I draw and how many counters do Fathom Mage and Toothy get after everything resolves?
When you're dealing with a complex situation like this, you need to just look at it step by step.As Bioshift resolves, it removes five counters from Toothy and wants to put them onto Fathom Mage. However, Pir's replacement effect steps in and increases that number by one, meaning that Fathom Mage gets six +1/+1 counters put onto it. This triggers Fathom Mage six times.As each of the Fathom Mage triggers resolves, Toothy will trigger. When each of those triggers resolves, Toothy will get two +1/+1 counters: One from the trigger itself and an extra one from Pir's replacement effect.When everything is said and done, you'll have drawn six cards with Fathom Mage, which will have six +1/+1 counters on it, and Toothy will have twelve +1/+1 counters on it in total.