I just picked two of them up this morning

I tested it and I was in fact not picking them up gas enough and they were disappearing. The problem was I was checking out their stats on the loot table rather than picking them up and examining them in my inventory.

Now I just pick them up right away

Now is there a guide that explains what these map effects do? Light effectiveness, more light, level up percentage… all of that is meaningless to me

Warm light effectiveness makes warm lights heal you for more.
Level up gives you that % chance to level up upon completion of the map.
More warm lights means more squares that will heal you.
Swarm gives that % chance to spawn another set of monsters upon defeat of the one you triggered by walking on a square.
I still have no idea what the stealth mod means.

Haha nice, thanks

I've since discovered whistling and been doing that instead. The two maps I found don't seem very useful and whistling is much faster!

Whistling is great for lower levels, but I recommend exploring at higher levels because you can only spawn EPs when walking around, and that’s where you’ll get a higher chance of a worthwhile drop. You also just have a lower drop rate in general with whistled mobs. That being said, I typically whistle from level 1 to 25-35 after completing the first maze for the +1/+2 extra equipment slots you get as a reward.

Great info!

What is an EP?

Evil Presence, it's a small "boss" monster, u will see a msg in the chat coming up whenever u spawn one

Map Mods that I know of:

Swarm: When you kill off the LAST monster in the Wave, it has a % chance to spawn a NEW WAVE of NORMAL monsters from +0 to +3 Levels of your Character Level. Note: when you kill an Evil Presence (wave), it can spawn a new wave of monsters (NORMAL ONLY).

Stealth: Best example: when the monster wave spawns, you have a % chance to attack them before they attack you. It comes in handy when you have little gear and come across a hard wave of Evil Presence, where you can go to town before dying, regen/shrine and re-enter catacomb, when re-entering, Stealth can come in handy to get in the first attack. Note: I have done this before on HC while facing Ambush.

A lot of the others that are important are self explanatory. As for +X Evil Presence and during an Event with +XXX% More chance of Evil Presence, the do not stack. Example: You map has +10 Evil Presence (meaning 10 unexplored squares WILL be an EP encounter) the +100% more Evil Presence does NOT mean that map will have +20 Evil Presence. Hope this makes sense.