About the possibility to delete monsters, I think it’s a very useless feature that caused lots of trouble for many players / accounts before. Where friends or children delete your monsters intentionally or unintentionally.
A non catchable monster, that can only be obtained once, should be fully excluded from deletion.
As an additional feature it should be possible to choose all monster evolution forms in any PvE event to overrule the problem of cost in their different forms.
To restrict players to switch evolutions in PvP, you could add a drop evolution function to set the monster back to form 2. To restrict permanent switching, just let the evolution ingredients and silver be lost if an evolution downgrade is performed.
Edit1: If the daily mission is called ‘perform a silver/youthfruit mission’, the Youth Fruit Mission Level 2 and Silver Mission Level 2 should be also counted.
Edit2: I would like to see the training section reconstructed into a training/testing room. A place where you can test your monsters, test your own monsters against teams constructed by yourself. Teams with a self adjusted buff + or - level, with variable teamlength. Add a monster moveset constructor where you can exchange monsters skills to test how a monster would behave with different moves, including additional moves or passives just for testing or fun purposes. All that stays in that training/testing room only or can be tested in ‘duel mode’.
I can remember the most fun before were games, where friends created a crazy racing track for you, you have to play it and afterwards you created one for him.
Edit3: Rework the team slots, there are just too few teams that can be saved. Possibly let the user create subgroups like PvE teams, PVP teams, WT teams,… . My poll that time clearly showed that this opinion was the huge majority.
Edit4: A shortcut/favorite function, like Raghnius suggested or in a different form. Due to the server loading times mentioned by aR0y2810, it can be a hassle to jump from home to a specific point inside the game. The bond shortcut was a great and very helpful improvement and it can surely be optimized further for other favorite/shortcut purposes.