- Attack with all three;
- Two mentor triggers go on stack;
- Stack triggers such that Blade Instructor's trigger goes first, have that target Boros Challenger;
- Boros Challenger's mentor trigger targets Goblin Cratarmaker;
- Both triggers see a valid target, therefore I end up with 3/1, 3/4 and 3/3?
I'm not sure if #2 actually works - it is possible that Boros Challenger's mentor ability won't trigger because it, at the time it goes on the stack, had no legal target (or does it trigger anyway, just not resolve?).