So, I am not particularly familiar with many of these categories, so I'm only going to look into and vote on the ones I
am familiar with:
[X] Plants vs Zombies:
Enforce-mint
[X] Enter the Gungeon:
Blank Companion's Ring
[X] Genshin Impact:
Guoba Attack
[X] Genshin Impact:
Kageroumaru
[X] Cassette Beasts:
Diveal
[X] Various:
Cujo (Danny Phantom)
[X] Jackie Chan Adventures:
Rabbit Talisman
Enforce-mint is just good cost efficiency. A pretty solid effect(10 random enemies nearby will be shrunk to a far more manageable size), and it's technically a modifier so we get a bonus creature to use it on(in this case the Kiwibeast)
Blank Companion's Ring is probably the best thing we can get from this category for only 300 points. It'll be up to Zagan to determine what constitutes an 'active item', but every time we use such a thing, the Blank Companion will nullify all enemy projectiles, and prevent more from being fired, for a few seconds. Very good way to create an opening in something like a gunfight.
Now about Guoba. Guoba may not seem particularly impressive, he's really not. But the thing is, he
used to be a God. Though it isn't going to be easy, we can potentially bring Guoba back to the level of power he once held. It's a storyline possibility even Zagan suggested for people who rolled him.
Kageroumaru is a very good boy so I'm putting him as an option too.
Take it from me, ASIMON may look neat, but it's really not that impressive for the cost. Below average for the 300 tier.
Diveal is good because it provides a permanent passive secondary buff. Domminoth and Jumpkin do too for the same cost but theirs just aren't as useful. Umbrahella would also be good, but more for the things we could take off of it than its own abilities.