My friend thinks that you can Replenish or Rector out a creature enchantment onto a Morphling, even if they activate its ability.
I say he can't. Who's right?
Yes, you can.
This is very counter-intuitive, but let's just say that the creature enchantment comes back as a permanent, and only spells (the ones you stack) have to pick a target.
Also, once you've started to resolve the Replenish or Rector ability, they have to wait for it to finish to get priority (to activate abilities etc). This played a role in David Zadok Stroud's extended post-necro deck which ran a pair of Confiscates to surprise opponents.
This reminds me: does making the Morphling untargetable in response to a spell or ability fizzle that spell or ability? around here it does, but I can't find exact rules one way or the other.
The term fizzle doesn't exist.
But yes, the result is that:
If you make Morphling intargettable after a spell targetting it (any spell with the word Target or a Local Enchantment) is on the stack, it will cause the spell to be countered upon resolution because it's target won't be valid on resolution.
You can see section 413 (particularly 413.2a) or the Comprehensive Rulebook for exact details about it.
Oh no! An anti-fizzler!!!
Fizzling was great...