A 5-mana black-red legend whose ability does one thing: force every opponent to take an extra upkeep. Nothing on its own — everything, in the right deck.
Upkeep-triggers value piles. Any deck running a stack of "at the beginning of your upkeep" effects (Bloodchief Ascension, Nekusar-style group hunt, repeatable card advantage engines) gets every one of them for free on every opponent's turn as well as its own.
Extort and drain. A deck already draining the table for small amounts turns a slow grind into a much faster one once every player is taking two upkeeps a turn instead of one.
Group slug / "everybody loses life" decks. Anything that punishes an upkeep — Bhaal-style triggers, symmetrical damage-on-upkeep effects — hits harder and more often once Obeka is out.
How it does in Commander
As the commander
As the commander, Obeka is a build-around rather than a value engine on her own — the deck exists to accumulate upkeep triggers and then cast her as the multiplier, so she's usually a mid-game payoff rather than a turn-one play. Being in the command zone means she's a reliable, repeatable threat the table has to answer or keep eating extra upkeeps from, which is exactly the pressure a group-hunt shell wants.
In the 99
In someone else's 99 she's a much narrower include — worth a slot only if that deck is already running enough upkeep triggers to make the extra upkeep matter, and even then she competes with better black-red payoffs for the slot. Most decks are better served leaving her to lead her own list.
Formats it's strong in
Multiplayer Commander pods with slow, grindy tables. Extra upkeeps compound across every opponent every turn, so the longer the game runs, the further ahead Obeka's deck pulls.
Decks already built around Bloodchief Ascension or similar upkeep payoffs. She's a direct force-multiplier on a strategy that already exists, rather than a new plan.
Formats it's weak in
Fast, low-interaction cEDH pods. A 5-mana do-nothing-on-its-own card that only pays off a few turns later is too slow against a table trying to win by turn four or five.
Any deck without a real upkeep-trigger package. With nothing to multiply, she's a vanilla 3/3 body that cost five mana to do very little.
Synergistic cards
Bloodchief Ascension — Every extra upkeep is an extra life-loss trigger and an extra step toward flipping it — the single strongest pairing.
Nekusar, the Mindrazer — Doubling upkeeps doubles the wheel-and-drain damage output of a group-hunt shell built around him.
Solemn Simulacrum — Straightforward card advantage that scales directly with how many extra upkeeps the table is taking.
Vorinclex, Voice of Hunger — Doubles counters and life totals that move on upkeep triggers, stacking with Obeka rather than competing with her.
Is it worth the price?
Obeka has stayed a budget-friendly commander — she was never a chase mythic and reprints have kept her cheap. She's worth picking up for the specific archetype she leads, and not worth a slot anywhere else: buy her when you're building the upkeep-triggers deck, skip her otherwise.