Basking Broodscale does not have a +1/+1 counter on it.
"Legion" chosen with Battle of Hoover Dam.

Activate Basking Broodscale's adapt ability by paying , putting a +1/+1 counter on it.
Basking Broodscale triggers, creating a 0/1 Eldrazi Spawn creature token.
Activate the Eldrazi Spawn by sacrificing it, adding .
When the Eldrazi Spawn dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Basking Broodscale.
Repeat from step 2.

You control at least one additional creature.

Activate Ashnod's Altar by sacrificing another creature you control, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ghave.
Activate Ghave's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

Once you have infinite +1/+1 counters on Ghave, you may target any other creature with Battle of Hoover Dam's trigger instead. You may also forego sacrificing the Saprolings.

You control at least two creatures.

Activate Ashnod's Altar by sacrificing a creature, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on a creature you control.
Animation Module triggers, causing you to pay to create a 1/1 Servo artifact creature token.
Repeat.

You control at least one Saproling.

Activate Utopia Mycon's second ability by sacrificing a Saproling, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ghave.
Activate Ghave's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

You control at least one additional creature.

Activate Phyrexian Altar by sacrificing another creature you control, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ghave.
Activate Ghave's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

Once you have infinite +1/+1 counters on Ghave, you may target any other creature with Battle of Hoover Dam's trigger instead.

You control at least two creatures.

Activate Phyrexian Altar by sacrificing a creature, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on a creature you control.
Animation Module triggers, causing you to pay to create a 1/1 Servo artifact creature token.
Repeat.

You control at least two creatures, one of which must be an artifact creature.

Activate Krark-Clan Ironworks by sacrificing an artifact creature, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on a creature you control.
Animation Module triggers, causing you to pay to create a 1/1 Servo artifact creature token.
Repeat.

Triskelavus has at least two +1/+1 counters on it.

Activate Triskelavus by paying and removing a +1/+1 counter from it, creating a 1/1 Triskelavite artifact creature token.
Activate Ashnod's Altar by sacrificing the Triskelavite, adding .
When the Triskelavite dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Triskelavus.
Repeat.
Once you have infinite colorless mana and +1/+1 counters, you may forego sacrificing the Triskelavites.

You control at least two creatures.

Activate Thermopod's second ability by sacrificing another creature, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on a creature you control.
Animation Module triggers, causing you to pay to create a 1/1 Servo artifact creature token.
Repeat.

You control at least one Saproling.

Activate Utopia Mycon's second ability by sacrificing a Saproling, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ulasht.
Activate Ulasht's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

You control at least one additional creature.

Activate Thermopod's second ability by sacrificing another creature you control, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ulasht.
Activate Ulasht's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

Once you have infinite +1/+1 counters on Ulasht, you may target any other creature with Battle of Hoover Dam's trigger instead.

You control at least one additional creature.

Activate Ashnod's Altar by sacrificing another creature you control, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ulasht.
Activate Ulasht's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

Once you have infinite +1/+1 counters on Ulasht, you may target any other creature with Battle of Hoover Dam's trigger instead. You may also forego sacrificing the Saprolings.

You control at least one additional creature.

Activate Thermopod's second ability by sacrificing another creature you control, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ghave.
Activate Ghave's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

Once you have infinite +1/+1 counters on Ghave, you may target any other creature with Battle of Hoover Dam's trigger instead.

You control at least one additional creature.

Activate Phyrexian Altar by sacrificing another creature you control, adding .
When the creature dies, Battle of Hoover Dam triggers, putting two +1/+1 counters on Ulasht.
Activate Ulasht's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Saproling creature token.
Repeat.

Once you have infinite +1/+1 counters on Ulasht, you may target any other creature with Battle of Hoover Dam's trigger instead.