So...

• For 4 mana, it's a Southern Elephant.
• For 5 mana, it's a Cultbrand Cinder that lets you look at the top card of your library.
• For 6 mana, it's getting better. It's like a Goblin Commando whose damage you can divide if you want (and is permanent), and it gives you a scry 2 but worse.
• For 7 mana, it's a Grim Poppet that you have to use all at once, and gives you Mystic Speculation but worse.

None of these are hugely exciting modes. I mean, Grim Poppet is great, and Goblin Commando is playable in Limited... but it doesn't strike me as hugely exciting. I guess it helps fuel a Reanimator cube deck? A little? Like, giving you Merrow Witsniper for 6 mana, or a single Millstone activation for 7 mana?

Seems like it could do with amping up a little bit, anyway.

Yeah, I wasn't sure about the balance of this card. Would X -1/-1 counters on each other creature be good?

X spells almost always look underwhelming when broken down like that (Disintegrate only deals 3 damage when you pay ? That card is terrible!). The point is that it gives you whatever you can afford. The fact that this compares close, but a little worse than Grim Poppet at 7 is more a cause for alarm, not a cause for dismissal. That said, me thinks this cube is more powerful than standard Magic, so it looks fine to me. I suppose only playtesting will give a proper result.

You say "whatever you can afford", but the big difference between this and Disintegrate is that this starts being an X spell at 5 mana, not 2.

But yeah, feel free to playtest it as is. Sometimes a Southern Elephant is what you need, and even Goblin Dynamo was okay in Limited.

It seems that often the question to ask with X spells is what role is this supposed to fulfil. If it's supposed to be an expensive-but-splashy 9-cost that's usually unplayable but is amazing when you can get it out, with the upside that you can play it as a midsize creature too, then it's quite good as is.

But if this is supposed to be a standard strong 4-6 mana creature with a splashy effect, it may be better to remove X and make a creature with the same effect that always costs 5 or 6 (or make the effect scale with something else)?

FYI, referencing X on an ETB ability when the X was in the cost doesn't work. You can try "When CARDNAME enters the battlefield, pay ...".

That's a really fiddly bit of rules oddness though. It even works for Verdeloth the Ancient.

Verdeloth is a weird case. I've heard some say it doesn't work, but Matt Tabak says it does. I think it's because kicker as a keyword can accomodate odd exceptions such as having the spell not target for the kicked part if you don't kick it (for example, Probe) while non-kicker spells like Cankerous Thirst have to target everything they mention.

Yes, it's weird and unlucky, but that's why my card Cauldron of Lost Souls has such a wording.

Hmm. Might just scrap the current card and start from the ground up, seems like the cons outweigh the pros at the moment.