If you see a pet that you want to buy multiples of in the store, you can buy as many of it as you want to, as long as you have all of the gems that you need. The first time you buy it, it will cost 25, and then 50 for the second time, and so on and so forth. Just make sure to buy all of the duplicate pets that you need before the timer on the store runs out.
This works especially well for any of the pets where tapping is multiplied when you equip it. Phobos is one of the pets that multiplies your tap damage; Hamy is, as well. Each time that you purchase a duplicate pet, you will level up the existing version of the pet. So whenever you level up Phobos or Hamy, you will increase their tap multiplier by 1 (such as from 2x to 3x).
If you are playing in a tournament mode, you can still prestige at any point. You will be knocked down in the rankings, obviously, but it’s sitll worth it to prestige if you have a good amount of time left, because if you get a better artifact, you could end up quickly eclipsing your old level high score in plenty of time to up your rank beyond what it would have been otherwise.
As always, remember that you can tap with more than one finger at a time. Not at the exact SAME time, per se, but you can alternate as many fingers as you want. If you are playing on a regular iPhone SE, four fingers at a time would be about the maximum. However, any larger device such as an iPad, and you can tap with about as many fingers at a time as you want to.
Some of the more obscure achievements include killing a specific number of titans. To do this one easily, prestige and then during one of the super early levels, stop the boss battle and just kill normal titans endlessly in order to rack up extremely quick titan kills. It’s a bit tedious but it works for free gems.
The first time that you can’t finish a battle against one particular boss, you will be off scot-free and none of your heroes will be killed. However, the second time that you lose to the same boss, there is a good chance that one of your heroes will die, too. So, lesson is, never lose to the same boss twice.