Solemnity was first released in the set Hour of Devastation Promos, illustrated by Greg Opalinski
The last is the nasty one that puts this deck over the top as a life-gain trigger for combos that you can never stop
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
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
After all, a three-mana 2/4 flier is often more than enough to slow down your typical Mono-Red Aggro decks
Note we're looking for the word destroy today, so no exile/sacrifice effects like Realm Razer or Cataclysm