Soul Knight

The premium currency is given from donating to the development team and is used on a selection of rare skins only avaliable through the premium currency.

Yes, but its generally additional content as the paid characters besides 1 don't necessarily provide an advantage just more diverse playstyles.

There is a limited time offer for new players but that doesn't really do much. However there has been a few skins and pets, usually from crossovers that have been limited.

The achievements generally do award geninue progress or unique challenges however there are badges that can be collected by grinding arbitray tasks.

Daily rewards are there, you gain a gem bonus as well as a higher-quality weapon to start with.

Earning gems via completing a certain amount of levels is necessary for character unlocks and upgrades.

Rather than grind for gems, you're allowed to purchase or watch ads to obtain the currency.

Different, more fun weapons can be unlocked via time investment (or P2W) as well as permanent character upgrades.

There is a list of optional achievements that unlock resource bundles or new weapons.

Although not a strong urge, there is a wall that shows each weapon you've picked up, as well as completion marks for each weapon and character.