Triton Wavebreaker

Bestow was built to answer a specific vulnerability: pour a spell into a creature and lose everything when that creature dies. The keyword's escape hatch is that the aura becomes its own creature rather than following the host to the graveyard, and here that safety valve gets pointed squarely at the prowess archetype, which is where the two halves start talking. Cast for a single blue mana, it is a fragile 1/1 that swells with every noncreature spell you cast that turn. Cast for its bestow cost, it hands the host both a +1/+1 boost and prowess of its own, so a spell-slinging deck's real threat grows every time you cast a noncreature spell. What separates it from most bestow cards is that the enchantment doesn't just protect the investment, it duplicates a mechanic the deck was already leaning on: the host learns the same trick that makes the standalone body dangerous. When the enchanted creature dies, the aura falls back onto the battlefield as a 1/1 with prowess rather than dying alongside it, so the two-for-one that open removal usually punishes leaves you with a permanent that still fits the game plan. It cannot re-attach from there (bestow is a casting choice from the hand, not something the creature form can activate), but a live blue one-drop with prowess is rarely dead weight in the deck it was designed for.