Sometimes when you get to the perk tower, one of the two choices will be to take a mascot with you to motivate your characters. While this can add some funny moments to the conversations between your characters, mascots are functionally useless. They cannot attack, and they add nothing to the attack power for any one of your characters.
The most valuable upgrades from the perk tower are arguably the heart and skull upgrades, because they give you more of hearts and skulls when your heroes prestige. Pick up the heart and skull upgrades in the castle, too, to make it so that every single prestige that you do is more valuable.
Most of the time you won’t need your magic skills, but they’re most useful as you are closing in on the natural slowing/stopping point before you prestige. This point is the point where enemies take inordinately long to kill. Bosses will be nearly impossible here, but wise usage of the magic skills will keep you in the fight and give you a chance to beat bosses more powerful than what you should be able to kill.
Make sure to spend all of your gold upgrading your most powerful hero/villain right before you switch armies. When you switch, the inactive army will still earn you coins when you don’t use them, and the more powerful your army is, the more coins they will earn you while you are not using them. The same thing is true for if you are offline as well.
Once you get an extra rank to your main hero (the one whom you control when you tap), it becomes unnecessary to upgrade it above a specific level anymore. Your hero’s damage will increase by a percentage of the total DPS of all of your other heroes and villains, so whenever you upgrade another hero, you will upgrade your main hero as well.
If a video shows up but then doesn’t play when you hit the button, try it again when you are outside or in an area with better internet reception. If there is a local wifi network and you aren’t connected to it, link up to it and try the video again in order to get the bonus.