Cauldron of Souls and Wickerbough Elder

Question

How many counters does Wickerbough Elder get when returned to battlefield with Cauldron of Souls? Assume that it died with no counters on it and was targeted by Cauldron of Souls. I can't tell if gets two -1/-1 counters or one when returned to battlefield.

Wickerbough Elder:

Wickerbough Elder enters the battlefield with a -1/-1 counter on it.

Cauldron of Souls:

Choose any number of target creatures. Each of those creatures gains persist until end of turn. (When it dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Answer 1

It enters with 2 -1/-1 counters.

Wickerbough Elder enters the battlefield with a -1/-1 counter on it.

is equivalent to

As Wickerbough Elder enters the battlefield, place a -1/-1 counter on it.

Similarly, Persist is also an ability that redefines entering the battlefield (ETB) to add the placement of a counter on the card.

Both are replacement effects that modify the same ETB event, so you apply them in the order of your choice.

For the card in question, the first replacement effect applied redefines ETB to add the placement of a -1/-1 counter. The second replacement effect applied then further redefines ETB to add the placement of a -1/-1 counter. Two counters are now placed as it enters the battlefield.

Answer 2

Wickerbough Elder will re-enter the battlefield with two -1/-1 counters in this situation. When it dies, it has two relevant abilities, it's own and the persist ability granted by Cauldron of Souls. Each of those abilities creates a replacement effect that causes it to enter the battlefield with a -1/-1 counter. Those abilities stack, so it enters with two -1/-1 counters.