So there’s always that one monster you can’t seem to catch, for me it’s Halobottle. Others might say this is just bad luck, because they have multiples of that ingredient monster, but I think it varies from players. Out of all the ingredient monsters per dungeon, there’s one that has a significantly lower encounter rate than the others. In my experience, I’ve caught/encountered 6 Flamebottles, 7 Seabottles, 12 Greenbottles, 5 Skullbottles, 9 Stormbottles and 1 Halobottle. Call this bad luck, but it has to be impossible to have such consistent bad luck. There isn’t much of a doubt that the devs have rigged this to have that one exceedingly rare monster, so that you keep playing trying to get it. Then if you keep playing, you might use gems to refill your tickets, increasing money flow to the developers if they buy more gems.
Yup that seems very likely. Also, bottles, pixies, and harps you can get outside of the ingredient missions. Just go to online missions. Bottle are in chapter 2, Pixies in 3 and Harps in 4. Holy Ruins Dungeon has a chance of dropping halobottles.
It’s all RNG. The RNG used on a mobile game is technically not pure RNG, but pseudo RNG, so there is a pattern, but it’s really difficult to find without cracking into the code. Just keep trying I guess, and if you still can’t get anything, try restarting your game to hope RNG won’t hate you as much next time. I seriously doubt the devs “rigged” it though, as pseudo RNG (the type of rng in games) in it’s own nature is almost rigged, as it can’t be truely random, because you’d need mercury leaking out of your phone. I wish you luck getting the materials you need 
I find games like this tend to have a higher chance to give you what you already have. Unfortunately for this game, they have a 256 monster limit. The materials seem to be included. They say it is for the old devices that can’t keep track of more than 256 monsters. But why apply it to materials that are all identical. Only one more byte is needed as a counter for each material. I am constantly deleting precious monsters to store multiples of the same material. Is this some sort of punishment for players that spend too much money?
If that’s truly the case then how about deleting a color u don’t need on purpose to take advantage of this “glitch”?