Sydri's power level on her own isn't there and she requires some setup, but her ceiling is high and you'll be able to make some sweet plays when she's on your board
Creature Artifact - Insect Color tag templates(None) Captain of the Watch Vigilance (Attacking doesn't cause this creature to tap.) Other Soldier creatures you control get +1/+1 and have vigilance
Simply put together your favorite White, Black, and Red vampires and go to town
My point is this: you have to think about it in the context of your own deck
While Riku isnt game-breaking, you get incremental value from Riku each time you cast a modal spell, which adds up in the long run
In a normal combat step, because both creatures have equal toughness and power, they would both die