Houndius Shootius

Deerclops hands out the one sentry you can place before Hardmode without touching the Old One's Army, and it costs nothing to keep running. That makes it free extra damage during the first tier of the event itself, where the Tavernkeep sentries are still competing for a currency you have to earn inside the event.

It anchors to the ground beneath your cursor, so aim at the floor where you want it standing rather than at the enemy. It fires slowly and one fireball at a time, which means it wants a chokepoint, not an open arena. Against a single tough target it out-damages the Ballista Rod. Against a swarm the ballista spreads better.

It pairs unusually well with a whip that adds its own hits, the Starcrash especially, because those bonuses scale off the sentry's large per-hit number instead of a fast weak stream.

Small thing worth knowing: the eye watches you until something enters range, then locks onto it. That is a free readout of whether the sentry has actually acquired a target.