The attack gained from destroying a monster is permanent.
It gradually gains attack.
It can prevent monster effects that activates upon getting destroyed by battle and then sent to the Graveyard.
Initial attack and defense is pretty low which makes it an easy target.
Having a low initial attack makes it hard to destroy a monster in battle in order to increase its attack.
Most level 4 monsters have higher than 1500 attack, making it difficult for Trainee to be able to destroy anything, but there are a lot of monsters with lower than 100 defense. Use position switching cards like Security Orb, or Enemy Controller to protect your monster so Trainee can destroy them without activating their "sent to graveyard" effects.
If your Trainee gets destroyed, you can use this card to special summon it back to the field, only recommended if you can use it to take down your opponent's monster.
Returns from your opponent's field to your opponent's Deck
This card gains ATK
Honestly this is the first time I'd gladly miss the gift event.
This card isn't even useful for Amazoness deck since it clashes with Onslaught's effect. If you banish, this card doesn't gain ATK, since the monster is treated as being banished by Onslaught's effect, not destroyed in battle by this card.
She isn't even good with heirloom either since that destroys by effect. She was kind of a fun card a long time ago. Like before Valiant Souls. But now with this and Amazoness Arena, Konami is just making fun of this since the deck is apparently never coming off the list. They should give us another queen instead.
I don't get the hate for this card tho. This card is great because it can be a threat for those who runs Blue Dragon Summoner (Last Gamble decks), Yomi Ship, Gravekeeper's Recruiter (need a booster like A.Forces to overpower the 1500 def.). I know that the stats are not great either.