No, this doesn’t work.
Each Primal Vigor and Corpsejack Menace have alternative results, not triggered skills.
614.1a Results that use the phrase “as an alternative” are alternative results. Most alternative results use the phrase “as an alternative” to point what occasions might be changed with different occasions.
614.5. A alternative impact doesn’t invoke itself repeatedly; it will get just one alternative to have an effect on an occasion or any modified occasions which will substitute that occasion.
When counters can be positioned on a creature, corresponding to with Mycoloth, each the static skills of Primal Vigor and Corpsejack Menace see this occurring, and substitute it with a brand new occasion. You’ll find yourself with 4 instances as many counters as you’d have had usually.
Particularly, you’d select the order to use the alternative results:
616.1. If two or extra alternative and/or prevention results are trying to switch the best way an occasion impacts an object or participant, the affected object’s controller (or its proprietor if it has no controller) or the affected participant chooses one to use
Say you play Mycloth and sacrifice 1 creature, so you’d get 2 counters. You select Corpsejack Menace first, so “put 2 counters on the creature” is changed with “put 4 counters on the creature”. Now Primal Vigor’s potential nonetheless has a “place counters” impact occurring that it might probably substitute. So it changed “put 4 counters on the creature” with “put 8 counters on the creature”. You find yourself with 8 whole counters, as a result of now there aren’t any extra alternative results obtainable to use.
Notice that for it to work the best way you counsel, you would wish a triggered potential, which might be worded one thing like this:
“Every time a number of +1/+1 counters are positioned on a creature, you might place that many +1/+1 counters on that creature.”
In the event you did management a card with this triggered potential (no such card exists), then you definately would not even want a second card with the identical potential… simply putting a single counter on a creature would trigger that potential to set off, after which the decision of that triggered potential would trigger that potential to set off once more. Perpetually, or as many instances as you want. Having 2 separate playing cards with that potential wouldn’t be meaningfully completely different from having simply 1 such card.
Enduring Scalelord is a really related instance; as a result of it says “one other creature”, it will not infinitely set off by itself, however in case you have 2 of them then they every set off the opposite as many instances as you need.
