Update: Sadly, this method no longer seems to work in recent versions of Terraria. Mannequins break instantly when lava makes contact with them. Statues survive the lava, but when water contacts it, obsidian is now created which displaces the statue.
Original answer: Okay, I've been poking it for a while, and have come up with a way to destroy any amount of water with just two items! This method does require you either tunnel around to get underneath the body of water you want to drain or stand in it while working, but it's still often faster than the old fill/dig method.
All you need is a mannequin (possibly other furniture as well, but something 2 blocks wide worked best in my tests) and a bucket of lava:
- Dig a 2 by 3 hole underneath — but not connecting to — the body of water.
- Place the mannequin in the hole, then drop the bucket of lava into it. Wait for the lava to settle.
- Dig a channel from the water to your lava hole and watch the water vanish!1
- Dig out one of the blocks supporting your mannequin2 and wait for the lava to settle.
- Pick your lava back up.
Sadly, you can't reverse the process to destroy large amounts of lava — the lava will happily hover above the water, never making contact, forming obsidian, or being destroyed. Worse, attempting to pick up this glitch lava will destroy your bucket!
1 The water vanishes because, when falling into lava, it should make obsidian. However, the mannequin prevents the obsidian from being formed (as they would occupy the same space) and the water is simply removed because it has no place to pool.
2 If you aren't close enough to your mannequin chamber before breaking this block, the mannequin may fall in the lava and be destroyed. Bring spares!
Best Answer
Statues (at least in my experimentation of building a fish farm) have a hard delay of about half a second before they spawn another monster, in addition to a limit on the number of alive monsters spawned at once (which is 3, if I remember correctly).
The optimal spawn setup seems to honestly just use a timer (one second, of course) hooked up to part of the statue, then a series of pressure plates near an area enemies are going to walk on. Reason being, their motion will try to trigger the spawn again instantly. This works especially well if you have it hooked up to a dart trap, as enemies will often jump at walls and retrigger the buttons repeatedly as long as they're trying to get at you, sending darts out all the time.
In my experimentation having more than two input lines in this setup doesn't change a whole lot in terms of rate of action.
One thing to remember is that wires in Terraria are not like Minecraft -- they do not have "on" and "off" states. They simply "pulse". So while a lever may look like it changes states, every time you click on it, it pulses a signal again.
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I will say, though, that I haven't experimented with multiple one-second timers. I don't think it'd do much other than provide a more reliable rate (if you can even get them desynced in the first place)...