Notes & Combos
Earthbound Runick, a simple deck but can have a high skill ceiling if played well. While I find the deck enjoyable, I would say they are not better than Naturia Runick and Runick Spright.
You want to play all the Earthbound Prisoners at 3 to have the highest chance of seeing tuners in your opening hand as Earthbound is only a small engine. Ideally you want to start with Ground Keeper (which you can also search by discarding Stone Sweeper) as it can special summon line walker which is another tuner. Linewalker then can get you Harmonic Synchro Fusion or Earthbound Prison. A one-off card that basically is Dragostapelia and Accel Synchron in one package. 16 Runicks minimum but you might want more
The jet in grave that you dumped can also act as a failsafe if you get nibbed cause the opponent has to Nib you after you summon Geri.
In the end you try to build a ***** to the wall board and then grind down your opponent with Runicks.
Tech cards such as Earthbound Prison just acts as a secondary search target for Line Walker who can also add them from the GY, it is decent for going second to break boards, and can also help extending. Earthbound Fusion is a weird card as it is unsearchable, it has a great GY effect which means that dumping it off from your hand with Hugin gives you more bodies and you can use it to summon Guardian Chimera on your opponents turn. However since Fountain is only at 1 and the ED space is tight, I decided to only run 1 with 1 Chimera in the ED.
Since the Earthbound engine is relatively small I decided to run 10 non-engine cards with 3 Ash, 3 Maxx, 2 Called by and 2 TTT which should give you a fighting chance going second and also help you play through HTs going first.
Regarding ED, you play at least 5 Runick monsters as you will burn through them quite easily, this should be 2 Hugin, 2 Geri and 1 Freki, this will change when Sleipnir comes. Marcher and Cyberse Integrator are for lines when you get handtrapped on your Hugin/Groundkeeper to draw cards and keep extending. The rest is pretty self-explanatory and serve to draw more cards with Stardust/Coral and Croc.
You can certainly change some spots to fit different Synchro LV such as Ancient Fairy/Pixie Dragon for LV7 or Omega for LV8, you can even run Masurawo as a LV12 target or Crimson Dragon with Dis Pater but those lines require lot of extenders.
I can make a more in-depth guide of combos with Earthbound Runick if interested and have a few replays in the Earthbound Channel.