It seems like, rather than a lifegain themed food deck (see the Food and Fellowship Commander precon deck), Ygra is poised to benefit heavily from mass artifact destruction, which might make her a seriously annoying commander to play against
Lastly, make sure your theft deck has lots of ramp
The price for the regularly-scheduled Commander precons steadily increased in the coming years before falling as they started releasing alongside Standard sets
Pair that up with the card Dark Ritual, which adds three black mana to your mana pool for just one mana, and you can drop the Specter on your first turn
In formats like Standard and Pioneer, decks built around cards like Ajani's Pridemate (or its more powerful variants) are usually competitive
She costs four generic and one white mana, has three power and four toughness