Creeping Bloodsucker

At the beginning of your upkeep, this creature deals 1 damage to each opponent. You gain life equal to the damage dealt this way.

Sphinx of the Second Sun

Flying
At the beginning of each of your postcombat main phases, there is an additional beginning phase after this phase. (The beginning phase includes the untap, upkeep, and draw steps.)

Descent into Avernus

At the beginning of your upkeep, put two descent counters on this enchantment. Then each player creates X Treasure tokens and this enchantment deals X damage to each player, where X is the number of descent counters on this enchantment.

Braids, Conjurer Adept

At the beginning of each player's upkeep, that player may put an artifact, creature, or land card from their hand onto the battlefield.

Twilight Prophet

Flying
Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
At the beginning of your upkeep, if you have the city's blessing, reveal the top card of your library and put it into your hand. Each opponent loses X life and you gain X life, where X is that card's mana value.

Obeka, Splitter of Seconds

Menace
Whenever Obeka deals combat damage to a player, you get that many additional upkeep steps after this phase.