Engine of the Goods are support hero monstors. They are cheap but very random. You roll 3 dice (or 4 with a Slann nearby) to see what the effect is. You can heal, do D6 mortals at 25″, summon extra units, or… if you roll three 6s, double all your army’s movement and attacks! Very good!!
Units That Synergise With It
A Slann is already a requirement for Seraphon armies, but you will want to camp the Slann near the EoTGs so you get an extra dice roll when determining their ability.
Use an EoTG in Thunderquake with two bastiladons. With Ethereal Amulet, you will have 3 unrendable monsters all rerolling their saves and healing D3 in your hero phase!
Magnetize the howdah so you can swap out the weapons and crew to change it into a Stegadon if needed.