Depends on the point value of the game and what your fielding tbh, for example a 1k list built around a Shadowstrike without taking the battalion won't do much.
You have to look at what the battalion gives you, is it worth saving the points to add more models to your starting army when you can always summon in with your Slann?
Not sure. Got tournament coming up and really stuck for list ideas. These are what I have built and ready Slann Astrolithe bearer Starpriest Oldblood /scarvet on carno (magnetised) Eotg 60 skinks 40 saurus spears 20 saurus clubs Sunblood 8 razordons 9 ripperdactyls 3 kroxigor 3 skink handlers 2 bastiladons lasers 15 chameleons
Something like this, Allegiance: Seraphon Leaders Slann Starmaster (260) - General Skink Starpriest (80) Saurus Astrolith Bearer (160) Battleline 40 x Skinks (240) - Boltspitters & Star Bucklers 10 x Skinks (60) - Boltspitters & Star Bucklers 10 x Skinks (60) - Boltspitters & Star Bucklers Units 6 x Ripperdactyl Riders (280) 4 x Razordons (160) 5 x Chameleon Skinks (120) Behemoths Bastiladon (280) Battalions Shadowstrike Starhost (180) Endless Spells Chronomantic Cogs (60) Balewind Vortex (40) Total: 1980 / 2000 Extra Command Points: 1 Allies: 0 / 400 Wounds: 120 @LizardWizard will have a better idea
Allegiance: Seraphon Leaders Engine of the Gods (220) Slann Starmaster (260) - General Skink Starpriest (80) Saurus Astrolith Bearer (160) Battleline 40 x Skinks (240) - Boltspitters & Star Bucklers 10 x Skinks (60) - Boltspitters & Star Bucklers 10 x Skinks (60) - Boltspitters & Star Bucklers Units 4 x Razordons (160) 3 x Skink Handlers (40) 4 x Razordons (160) Behemoths Bastiladon (280) Bastiladon (280) Total: 2000 / 2000 Extra Command Points: 0 Allies: 0 / 400 Wounds: 130
Bases on that I could take this as thunderquake. Slann Eotg Astro 40skinks 10 skinks 10 skinks 4 razordons 3 handlers Bastiladon Bastiladon 5 chameleons Thunderquake. Then spend the rest of the week building skinks
I like this list. Give your EotGs a survival artifact. Competitors at big events normally know to kill the EotGs in a Thunderquake list. @Crowsfoot's Shadowstrike is also solid. Like always; bring more Razordons