Krenko, Tin Street Kingpin grows in size over time, and makes more Goblins based on how big he is
however, they also have menace
The other ability is a Magecraft trigger, which is one of the new mechanics from Strixhaven: School of Mages, that activates whenever you cast or copy a sorcery or an instant
The additional line of text on Murktide Regent just makes them unnecessarily big sometimes, as additional instants and sorceries that get exiled, give him more and more +1/+1 counters
And bouncing has a lot of flexibility as a way to survive removal or blocks, adding a useful tempo element, reloading a creature with a powerful enters-the-battlefield trigger, dealing with auras and so much more
If, however, one creature has first strike, that creature is given a first chance shot at knocking the other creature out with impunity: if the creature with first strike can kill the defending creature, the defending creature dies immediately, even if the defending creature would otherwise kill the attacking creature