Kicker would fulfill Subchallenge 1. I didn't mean main challenge.
I agree my words in the Elegance section don't convey my stance correctly. Let me explain.
This particular ability appeared recently on Brawler and Pale Rider of Trostad. There's no card in Magic that has your cost. Why?
- When possible, additional costs like this on creatures are replaced by ETB abilities. Many cards have ETB, so it's easier to remember how you should play with the card if it's ETB.
- There are around 17 cards with similar text in Magic. Each has its own reason to be created this way. Firstly, if it is related to mana cost, it needs to be done when casting, of course. This explains Bucanneer and similar, and Torgaar. Secondly, there are two cards from Dragons of Tarkir (Orator of Ojutai). They have very strange text for a reason - to unify how they work and make sure you can't deny this bonus. Thirdly, skaabs. For skaabs, their whole deal is having a downside being a cost you need to pay to get an undervalued creature. It's easy to not have a creature in a graveyard to exile. If they have ability like brawler, they would be crazy good. Finally, Demon of Catastrophes. Its situation is similar to yours, right? Well, I don't think so.
- Final decision how a card should be templated should be made by gameplay implications. There are multiple ways to template very similar things. What is the best? For Demon, it's cast cost, as it would either need to sacrifice itself if it ETBed, or be too good if it said "another creature". For Brawler and your card, as I said, it would be a terrible topdeck, and it doesn't need to have additional cost to work correctly. Thus, it should default to ETB ability.