Your best late game strategy?

[Norfleet]

Well, for late game, there's nothing like finding an Alteration bonus magic site and summoning Doom Horrors. That's a fairly economical instant-SC right there, and a single Doom Horror can tear apart just about any normal AI opposition.

The drawback being that Doom Horrors appear to cause bad events in the province they occupy, so you'd best ship them out quickly and get used to the lab burning down every few turns.