As pointed out by others (seems I was mistaken in my first post) you can curate your spells to minimize randomness.
0-3 slots may be harder to curate since you may want to run multiple different low cost spells to survive the early game, but I’ll list the non-random or at best semi-random ones anyway (this list is not exhaustive, I’m doing this quickly and not double checking if I missed anything)
0 mana
-coin
-snake oil
1 mana
soulfreeze (semi-random, a worse version of dawngrasp recasting flurry, but just like flurry, end result is probably a net gain, freezing stuff that might otherwise kill you next turn)
shooting star (semi-random on who it hits, but it’ll be an enemy)
flame geyser (very meh damage but not random)
2 mana
cryoprevervation (one of the better ones of all the low cost spells)
heat wave (a bigger shooter star)
Rewind (semi-random, but you can curated your spell which means you limit what spell you rewind)
3 mana
Elemental companion (semi-random, but you know it’s a minion, not sure if the spells will be cast in order but if this casts first, and you get spell damage, then the rest of the spells from orb should benefit)
Secrets (semi-random to completely known if you only run/play one secret all game)
Lightshow (semi-random scaling damage)
Molten rune (the damage is good but the spells it generates might mess up your spell pool)
Reverberation (at minimum makes the enemy minion easier to kill; bonus if you end up being able to use the copied minion)
Sludge
Arcane intellect (ok probably won’t be run but listing it lol)
4 mana
Fireball
Volume up
5 mana
Wisdom of norgannon
Star power
6 mana
Blizzard
Chaos creation is super risky and there’s always a chance for the random 5 drop to be a dud, but the damage part is consistent.
7 mana
Flamestrike
Firelands portal
Elemental inspiration (though if you’re curating spells hard you may not want to run this, since you may not be casting as many spell schools in fear they mess up your orb)
8 and 9 mana I see nothing right now
10 mana
Sunset volley
Orb itself again (not sure if it can recast itself)
Based on this second scan/analysis, orb may go in a big spell mage deck, where you drop most/all low cost spells and favor the 5+ mana spells which are fairly consistent. If you can get like 3 big spells off before casting orb, the orb should be worth the cost.
The only small spell I’d run would be cyropreservation. If orb recasts it, cool. But it could also recast a 2 mana treasure spell which should still be useful. And if your other excavates gave you a 1 mana or 3 mana spell treasure, well orb recasting those is also cool.