While resolving Nadir Kraken's ability, you can't pay {1} multiple times to create multiple Tentacles or to give it multiple +1/+1 counters.

You choose whether to pay {1} after drawing the card and seeing what it is. If you draw multiple cards, you see them all before deciding how many of the resulting triggers you'll pay {1} for.

If Nadir Kraken leaves the battlefield after its ability has triggered, you can still pay {1} and get a Tentacle, even though you won't put a +1/+1 counter on Nadir Kraken.