Er'cana can be soloed as well. You need to be speedy though. I'm not sure if I would spoil anything here so to make sure I'm not getting the fun part out of your gameplay or anyone else's gameplay, I will put the description inside a spoiler.
- Show Spoiler
To solve Er'cana 4 symbols puzzle, you need to reach the 2 storey bahro caves, one entry is through Er'cana, one is through Ahnonay. The real way to solve it is for you to enter through Ahnonay's entrance linking you to lower level where the symbol will appear, your helpmate will enter through Er'cana's entrance with a pellet in its hand, the pellet will be dropped from the upper level upon entrance and it will highlight the symbols on the wall on the lower level where you should be standing.
Now, how do you manage to do that solo? Well, you need to be quick on your feet. You go and drop yourself a pellet, you run to the other side of the opening where the pellet was dropped and you jump against the edge to discover the symbols highlighted on the wall on the lower level. It is good to have memorized the 7 possible symbols beforehand. Now, don't expect to spot them all 4 unless you are a hawk. Mathematically, as long as you have 2 out of 4 symbols, it is quite an easy task because then you have to parse through 20 possible solutions in the Cleft. 7 symbols, 2 known, 2 unknown, 5 times 4 = 20 possibilities
If you spot 3 of the symbols, then it is much easiser, you have to parse through 4 possibilities. 7 symbols, 3 known, 1 unknown, 4 possibilities
The best way though to achieve that feat is to record yourself while you are jumping, you then go through the small video (it can be a duration of 20-30 seconds only) and you stop where you can spot the 4 symbols highlighted, there you go!
Remember that the symbols go to a specific spot, if one symbol is at the top, it goes there, etc.