This could end up better than Grand Market for one player and a Navigator Bureacratty thing for another!
Here are some ideas to make it less swingy:
1. When you discard it from play, if you have 3 boons set aside, the player to your left picks a boon; you discard that boon.
That's very wordy, though, and the card is already full of text. No more Saboteur squint-o-vision plz
2. Have a shared pool of set-aside boons (maybe 4 or 5 instead of 3). When you play Offering, you may discard one of them. When you discard (or maybe that should be play) Offering, you may add one if the limit hasn't been reached. [Maybe the discard option should only be there if the pool is full.]
The benefits are symmetrical, which is very different from the posted Offering. It fixes the "You got Swamp and Flame while I'm stuck with the lousy ones" problem. In case of a non-mirrored strategy, it lets you steer the pool towards what uniquely favors your strategy (but your opponent gets to do the same to you).
It also doesn't dry up the Boons deck, so it interacts with
Druid and other booners less b0rkenly.
If "look at the top card of your deck, you may discard it" and "draw cards until you have 5 cards in hand" were things, this could be a Jack of all Boons