Caldera Hellion: For the beatdown plan if you trigger DotH when against an opponent who runs heavy removal (and would just kill Maniac then watch you deck out). Grabbing this guy and a Hunted Troll will probably wipe the board in many cases, leaving you with 11 power unopposed. If you find that 3 dmg isn't enough to sweep, you can run Crater Hellion instead.
About the hellion, I would play Avatar of Might an over it since it is an 8/8 with trample. Also it becomes a creature for

with all those tokens I I’m producing. Which I think is a better way to put pressure on them.
The additions and changes I would make to your revision Delha are:
Remove the hellion, add an Avatar of Might
Add:
4x Miscalculation
This is another counter in addition to being a source of card draw. It has good synergy with the maniac
4x Edge of Autumn
Mana Fixing, and Cycling.
3x Gush
Foresight, malipulate fate might work here too
Avatar of Might is far inferior to Massacre Wurm (which should replace Hellion per vaughbros' suggestion).
1. You don't want to be hardcasting here. The idea is to dig up Wurm via DotH.
a. Wurm + Troll gets you 14 power, kills their dorks (Welder/Confidant/etc), and deals probably 16+ dmg in the process.
b. Avatar + Troll gets you effectively 8 power on the board (since Troll gets chump blocked for four turns).
c. Using Avatar to attack means you want to race, but leaving they with tokens makes it harder for you to do so.
2. Avatar only works with Phantasm. Troll gives them only 3 more creatures than you.
3. If you trigger DotH off a Phantasm, you can dig up Phantasm + Wurm for lethal. 5 tokens from each Phantasm = 10 tokens = 20 life.
4. You want to get rid of their tokens if you're going beatdown, to stop them from outracing you.
What's the rationale behind Foresight/Manipulate Fate? I may be missing something, but both seem worse than Lat Nam's Legacy in this deck. Gush could work out well, and Edge of Autumn might be okay, but I'm dubious about Miscalculation. I suspect it's too weak of a counterspell, meaning that it's likely going to just sit in hand a lot waiting to be cycled. If that ends up being the case, you're better off running something else. Maybe Abeyance, Fire/Ice, Remand, Repeal, or even Call to Heel. I'd probably personally lean towards Call to Heel/Repeal. The former stops BSC, and the latter is good for just general utility.