Brain of Cthulhu
In my opinion, pre-boss mages and summoners are pretty lacklustre. They aren't particularly powerful until you defeat Skeletron and the evil biome bosses, and their weapons at this stage are pretty difficult and/or time consuming to get, whereas melee and ranger have weapons that can be obtained relatively quickly. 1.4 and 1.4.1 have helped out summoner a lot, but not much at the start of the game. Here are my suggestions to make these classes viable throughout Pre-Hardmode.
This weapon is decently powerful, but it is too rare. Wooden Chests are very limited, and if you're unlucky there won't be enough near spawn, meaning that you'll have to cross very dangerous biomes such as the Corruption/Crimson or the Jungle, for a weapon that might not be there. I think that it should instead be crafted with 15 Wood and 5 Torches, because that would allow you to make it quite quickly.
The issue with this is similar to the Wand of Sparking's issue, except more extreme. Living Trees are rarer and much more limited than Wooden Chests. To make it easy to get, Living Trees should always generate close to spawn and at least one Finch Staff should be guaranteed in every world.
This is way too rare to be useful. So that it doesn't have to compete with the Flinx Staff, it should become a King Slime drop, like how the the Blade Staff was moved to Queen Slime's loot pool, and have a big DPS increase to make it better than the Flinx Staff.
This is too expensive for its stage of the game, so it's usually faster to just get the Snapthorn. Its price should be lowered to 5 Gold, so that it can actually be useful.
This was probably intended to be a crowd control weapon, but because of the minion's AI it doesn't reliably hit multiple enemies in one shot. The minion should align itself horizontally before firing. It should also get a damage nerf. This way, it would become a great choice for tier one Old One's Army, and would compete less with the Hornet Staff.
This would be a very weak whip that would exist to give you a way to tag enemies at the very start of the game, and help with completing 10% of the Bestiary to get the Leather Whip. It would be crafted with 6 Iron/Lead Bars and 5 Chains.
This staff would summon an Antlion Swarmer minion that would be a flying melee minion that serves as an upgrade to the Finch Staff. It would be crafted with 5 Antlion Mandibles and 15 Sturdy Fossils.
This would be a sentry-summoning staff that would summon an Antlion that fires balls of sand at enemies. It would be crafted from 5 Antlion Mandibles and 10 Sturdy Fossils.
Icefall would be a spell tome that would drop from Ice Bats and Spiked Ice Slimes in the Underground Snow biome. It would spawn icicles above the cursor that would fall onto enemies, dealing damage.
This would be a magic gun that would inaccurately fire high-velocity spores that would be unaffected by gravity and burst upon hitting an enemy. Upon colliding with a solid block, the spores would bounce back and drift downwards. If an enemy is nearby, any drifting spores will home in to them and burst on impact, similar to what the spores fired by Giant Fungi Bulbs and Plantera do. The Spore Spewer would be crafted with 8 Jungle Spores and 10 Gold/Platinum Bars.
This would be a summon weapon that would summon a small Eater of Souls. Similar to the Blade Staff, the Eater would deal damage at a fast rate. This would be dropped by Shadow Orbs.
This summon weapon would summon a Face Monster that would function similarly to the Pirate Staff. This would be dropped by Crimson Hearts.
The Vile Scepter would be a magic weapon crafted with 10 Demonite Bars. It would fire homing non-piercing Vile Spit projectiles in a similar fashion to the Spectre Staff.
This magic weapon would be crafted with 10 Crimtane Bars. It would fire a red projectile that would travel in a straight line until it hits something. If it hits an enemy, they would get a debuff that reduces their damage and their movement speed by increasing amounts the lower their health gets. Bosses would be immune to this debuff.
Black Lash would be a whip crafted with 10 Demonite Bars. It would apply a special debuff on enemies that would make them able to take damage from other enemies.
This whip would apply a unique tag effect that would make minions reduce tagged enemies' stats by a small amount every time they deal damage to them. The reduction in stats would depend on how much damage is dealt. It would be crafted with 10 Crimtane Bars.
The Inferno Burst, a magic weapon crafted from 15 Hellstone Bars, would be a Pre-Hardmode version of the Resonance Scepter. It would act almost identical to the Resonace Scepter, however it would create bursts of fire instead of glowing pink circles.