DoJ is useful for many reasons.
1) It avoid Meddling Mage.
2) It allows you to regenerate your own creatures if you so desire.
3) More often than not, the regenerate clause is pointless.
4) It's cheaper.
Only 1 and 2 are legitimate reasons, and 1 seems like a stretch.
These are all great suggestions, and pretty creative, but if you just want a simple way to permanently deal with Progenitus I would recommend Final Judgment.
I like the hybrid version, but the nonland clause should definitely stay. Otherwise, too many people will randomly lose to this after keeping a reasonable two lander.
That time walk ability is effectively a -1 because of his +3. I know that six mana walkers are basically impossible to break, but it still makes me feel pretty nervous.
Also, what is the starting loyalty supposed to be?
I think the lack of a may on landslide makes it really painful in some situations without helping much.
I agree that pebblemite is probably too powerful. R is much better than 2 for mountaincycling, because it makes far more one landers keepable.
The most egregious card in my opinion is spastic arc, because you can play a deck with few creatures that die too it (or none). In such a scenario, Lightning Bolt, Arc Lightning, and Char make it seem much more fair at cmc4.
I do really like the shock, bloodscurry, lava blast, faultline, and grounscour.
On the subject of costs, I think 3 to play is good.
I don't know if this is as simple as you want, but my first thought for activation was 7, minus 1 for each card in that opponent's hand.
It scales even better with Thallid. Or Mycoloth if you're feeling particularly silly.
Only 1 and 2 are legitimate reasons, and 1 seems like a stretch.
Also, Holy Light seems more like a sideboard card. I'd try Homing sliver in that slot.
On the subject of Harper's entwine version, I think upping the initial cost past R would suck. A good entwine cost is probably RR or 2R.
Also, what is the starting loyalty supposed to be?
I agree that pebblemite is probably too powerful. R is much better than 2 for mountaincycling, because it makes far more one landers keepable.
The most egregious card in my opinion is spastic arc, because you can play a deck with few creatures that die too it (or none). In such a scenario, Lightning Bolt, Arc Lightning, and Char make it seem much more fair at cmc4.
I do really like the shock, bloodscurry, lava blast, faultline, and grounscour.