You essentially draw a card on attacks, but you get to cast that card for free if you built your deck with mostly odd mana value cards
The main purpose of split cards is to offer options for players, usually combining narrow effects that wouldnt be playable by themselves
Valki, God of Lies / Tibalt, Cosmic Impostor For the purposes of theft strategies, we're much more interested in Tibalt, Cosmic Impostor than Valki, God of Lies
Unlike most red rituals, Seething Song was so strong, it was actually a staple in fair decks, literally just looking to play cards that cost five or more two turns ahead of schedule
Play Sephiroth if you have some sacrifice fodder around to reap the benefits
Of course, you need a lot of investment, but it's an option if you ever want to venture on this route