AoS How can I use my Engine of the Gods?

[N1nj4]

So I'm fairly new to AoS (I've played 40k for a while and I thought I'd give it a go) and I recently bought an engine for my seraphon. I decided to test him out the other day with a game against a nurgle demon prince, and a couple nurgle heroes. I read through the rules before the game and felt pretty confident that I was going to win (3D6 Crushing Stomps, being able to summon units and take another turn sounds pretty good). Well let's just say at the end of the game the only thing I had alive was the starpriest I summoned ( I only have skink units right now :/ ) Am I using him wrong? Plz halp D:

 

[Bowser]

Best use would be sitting him near a slann and a skink starseer, roll your four dice from the slann and use curse of fates on it from the starseer. Up your chances to get the roll you want, it's more useful as support than as an attacker.

 

[Killer Angel]

As said, EotG is a heavy support unit, that can say a couple of things in combat, but its main use is to help the army with useful and unique abilities.
You absolutely need to keep near a Slann, to roll 4 dices. If Kroak, you'll also have a nice reroll, but it can be done also with a Starseer.
So, cosmic engine.

Summoning is not exactly a trap, but it's not so useful. You already have Slann for summoning, it could serve just to call big things (Dread Saurian? ).
The real good abilityes come with 18+ (free turn FTW), 6-9 (d6 mortal wounds is huge), and also 10-13 (when the enemy surrounds you)