Yes. There are actually a few pretty powerful ones.
One that I’m using right now is the death spell, ‘Living Dead World’. Combined with the ‘Living Dead’ battle spell it can be pretty ugly for opponents. What happens is that any time you kill an enemy unit, it rises as a random undead unit and fights for you the rest of the battle. After the battle, you get to permanently keep as many of those surviving undead units as will fit in your army. So if you keep 4 spaces empty in your unit stack, you essentially get 4 free undead units every battle. Talk about force multipliers. If any AI has that up, it’s a priority dispel for me.
Another one is the arcane spell, ‘Time Warp Bubble’. You cast it on a tile and then it has 2 effects. First, there’s 0 movement cost in the hex. Second, and more importantly, the deity owning the spell can cast 2 battle spells per turn rather than one. That second effect is very powerful and I’ve seen some people on the Steam forums bitterly complaining about the AI being able to cast twice per turn, not realizing it has this world spell in effect.
You may wonder what good it is if it only affects one hex. Well, if you cast it on your best city’s main hex, it makes defending the city from attacks a whole lot easier. You can also cast it multiple times (it cost 5 mana per turn to maintain for each iteration) so if you have tons of mana you could actually make a zero movement cost road with this spell.
There’s also the ‘Slow Time Bubble’ spell which is similar but reduces other deities ability to cast in combat to every other round. I wonder if you could stack the two? It would be pretty devastating.