An avocado grown from a pit in water can keep going for some time but it's not an ideal situation. The pit is there to feed the embryo seedling as it gets established, but the plant will expect to start feeding from roots and leaves as soon as possible. I put one of my potted avocados outside on the deck once, a squirrel came along to investigate, pulled off ...
This is not mould this is a plant living in water and the roots are calcifying and eating through these this will not harm your plant my brother has many of these and so do I not a worry if you actually look at some of the seeds they actually have a mould growing around there that's different to what is growing on the roots
Alocasias have bulbs and can be grown from bulbs, How to grow an Alocasia from a bulb. So what you have found in the pot are unsprouted Alocasia bulbs.
These plants often could go dormant, loosing all of their leaves and becoming a stump just to regrow from the bulb next spring.
Here is an Alocasia bulb from the article above.