The Denizen offers some easy evasion, which helps you attack through big green creatures or other annoying blockers like Reflector Mage but ultimately isnt that powerful, especially when topdecked in the mid- to late-game
Venat, Heart of Hydaelyn / Hydaelyn, the Mothercrystal In commander the name of the game is legendary spells, so planeswalkers and cards you already want in your white deck like Flowering of the White Tree and Caduceus, Staff of Hermes, get much better with Venat, Heart of Hydaelyn in play
The drawback is that you need to cast cards to get more cards, and Sunbirds Invocation is extremely expensive at six mana
But it struggles against removal-heavy black midrange decks like Dimir since we really need to be able to keep two or three Frogs on the battlefield to get our value engine running, and the endless removal black has to offer is pretty good at keeping the board clean