Regeneration cannot save the creature with toughness 0 or less
Lore-wise this is actually a wizard who's fallen victim to mana burn, a now defunct rule in Magic which made players' own unspent mana deal damage to them
As per Frogifys flavor text, a gnat was still hovering by the venison, and now both looked delicious. 2 | Infernius Spawnington III, Esq
in cEDH, Blood Pet is often found in Krrik, Son of Yawgmoth builds as a way to net an extra mana for 2 life, but also sees a lot of play in Inalla, Archmage Ritualist and Ad Nauseam lines to rush out these expensive spells or aid in comboing off with other cards to win the game
After all, a three-mana 2/4 flier is often more than enough to slow down your typical Mono-Red Aggro decks