Lifegain is a popular mechanic among Commander players (at least very much among the players that I know), and a simple 4-drop that not only shuts off all lifegain but reverses it into life loss seems like an extremely powerful effect to me
Still, 5 mana is a bit much for this effect
While this ability isnt specific to Insect decks, Xira herself is an Insect, which allows her to benefit from any Insect synergies you include in the 99
You can give them one loyalty to create a 1/1 Insect token, mill a card, and then repeat the process if the milled card was an Insect
The best way to go about it is to buy all five decks in one go and save Gavi for a later date to re-sell
Bloomburrow Bundle As with previous MTG expansions, Bloomburrow launches with a bundle full of boosters to introduce you to the expansions new cards