It's not necessarily Orc but getting your damage up and not relying on your mana pool as much. Mage Plate still works because -% damage does nothing to Pissorff, allthough it's kinda better to start out with the ball and find IT in the shop, because it helps you ding, and keeps your damage high until the right moment. Flames are hardly necessary. Orc Sorcerers and especially Orc Bloodmages can both level and unload Pissorff spam.(Wizards with the ball are obviously good Pisorff guys, but noone goes really nuts with that thing quite like a bloodmage does. You can get your damage up really early, get your health/b2p cost low at lvl1, never push anything into blackspace and spam. The only reason you can't lvl1 ding is because you refuel by munching on popcorn).
And, nope, 2X damage fireballs with max burning from fireball one is actually the best against retaliate fireball, bar nothing in almost any circumstance no contest, not close. Especially paired with EM where your mana pool size becomes irrelevant. It takes very little in terms of general spellcasting optimization (a loaded fire heart is good though), what you need is a platemail or some resists to further lower the already halved damage you're taking from retaliation (elven boots help with that, and so do GG beads and obv. protections). Codex EM clears Cursed Oasis like nothing else (really, it's like you're not playing the same game), and Codex wizard with Extra Glyphs can easily find Wonnafyt to take care of the Matron. Sorcerers already > Elves for everything but making your life more difficult, and heal a bit when casting stuff, and if you're a goblin you convert for full heal.
Technicaly, Pissorff Bloodmage, Goblin Sorcerer and Codex/EM Halflings are what I consider "standard spellcasters", if you're putting effort into either replenishing your mana or incresing your mana pool as a spellcaster (or indeed at all), you're being a hipster. XD Essentially, if you're mana pool size isn't "solved" from tile 1 (in the sense that you know the exact number and are sure it's guaranteed and 0 effort will be put in and everything that happens to put it over that is just 'cause) you're probably overdoing it ^^
And also, I'm not sure there's another item which once you locker it changes the game as much as Avatar's Codex. It turns otherwise difficult dungeons into lol-stomps and supremely unsynergistic PQI's (a surprising number of them) into lol-stomps. Codex/EM is like an expansion pack for the game all on it's own.