Nice! Two things:

• This currently has Dogged Hunter's ability almost by accident. Do you want "nontoken" in there too?
• With Sky Hussar or similar, this gets you every card of CMC 4 or less from your deck, and then stacks the rest. In fact, come to think of it, this goes infinite with both Kiki-Jiki / Splinter Twin and Pestermite / Deceiver Exarch, doesn't it? That takes some doing!

Beautiful. I understand Alex's Dogged Hunter comment, but I'd suggest against using nontoken. There's no reason why this can't exile token creatures, especially being mythic and all. Just extra words to process.

The only think I might add is this ability probably costs more than WUBRG... especially with haste. Considering you could 'EOT activate, activate on my turn, Disperse Maelstrom Djinn.' You could even bounce the Djinn in response to its own ability, guaranteeing your opponent can't recast the permanent, even if it has flash. (that said, it's Mythic. I still don't know what the rules are for that rarity. Maybe it's 'do as you please'?)

I do appreciate, however, that this card can protect just about everything but itself. If it exiles itself, you can't cast it. That's going to get a lot of people calling 'judge!' at a tournament... perhaps this needs reminder text that says "(as long as ~ is on the battlefield.)" Also, this might need the Legendary type. It would get really annoying trying to remember which djinn exiled which spell, so if one got removed, I knew which spells I could and could not cast from exile.

Huh? I think you've misunderstood the rules a bit, jmg. This allows the permanent's controller to recast the spell right now, during the resolution of its ability; if the controller chooses not to, then it's stuck in exile for ever. So the comment about Disperse and "which Djinn" don't apply. And it would be able to recast itself, except that the ability says "another".

Huh. Actually, it's kind of ambiguous. Chandra, Pyromaster says "this turn" and this card does not. I suppose the default assumes it's happening in the middle of the ability's resolution? Seems weird to me... but the timing on Panglacial Wurm seems weird to me, too.

To be honest, my mind automatically clicked onto what I assumed was the 'weaker' of the two versions. With Alex's version, this roughly says ": Exile target non-land permanent your opponent controls." which seems even more OP to me. Or can your opponent now cast that creature in the middle of this card's resolution with or without flash? Hmm. Weird. It's not that I'm not cool with all that, but it seems to fight the way my mind is used to playing Magic. The card seems counter-intuitive, but only to a certain segment of experienced players. New to intermediate players will probably grok it immediately. How odd.

It's not ambiguous, but it is confusing. There are two similarly-templated kinds of abilities with very different results. If a card says one of these:

• [player] may cast that card [duration]
• [duration], [player] may cast that card

(e.g. Chandra, Pyromaster; Daxos of Meletis; Narset, Enlightened Master, Stolen Goods) then it sets up an effect that allows the player to cast those cards at a later stage. And they do have to respect normal timing rules. On the other hand, if it just says

• [player] may cast that card

(e.g. Epic Experiment, Knowledge Exploitation, Spellshift) then the player gets one opportunity to do the casting, right now as the ability is resolving; if they don't then they've missed their chance. But they don't have to respect normal timing rules (because after all, you can't normally cast spells in the middle of other things resolving anyway).

So this doesn't say ": Utter End" for the same reason Descendants' Path can work at all - because the ability gives you a chance to cast things right now, even if you couldn't normally cast that creature spell in your upkeep.

Alex is completely in the right here.
The power level is a bit bonkers. I should probably cut the haste and maybe even require paying the exiled card's cost.