But an indestructible creature is put into a graveyard from play as a state-based action if its toughness is less than or equal to 0, and -1/-1 counters can achieve that
It is not the most reliable of pure life gain effects as all kinds of removal can really set you back in tempo and will therefore almost certainly finish you off given that you were trying to gain more life

Academic Dispute Academy Raider Accelerate Akki Ronin Akki Scrapchomper Akoum Flameseeker Aleatory Amber Gristle O'Maul Ambitious Assault Ancestral Anger Arterial Alchemy Artist's Talent Ashling, Flame Dancer Ashling, Rekindled Axiom Engraver Balduvian Rage Battlefield Scavenger Bedlam Reveler Belligerent Guest Bestial Fury Big Score Big Wheel Bitter Reunion Blindblast Blood Petal Celebrant Blood Sun Bloodfire Mentor Bloody Betrayal Boiling Blood Boundary Lands Ranger Brand Brass's Tunnel-Grinder Burning-Tree Vandal Burnout Case of the Crimson Pulse Chandra's Defeat Chandra's Regulator Chandra, Spark Hunter Change of Fortune Chaotic Strike Charging Strifeknight Charming Scoundrel Clamorous Ironclad Cleansing Wildfire Cloudpiercer Common Iguana Conspiracy Theorist Cool but Rude Crash Through Crimson Wisps Cunning Maneuver Curse of Chaos Day of the Moon Decaying Time Loop Decree of Annihilation Deem Worthy Demand Answers Demonic Ruckus Desert Cerodon Desperate Ravings Destructive Digger Discerning Peddler Dismissive Pyromancer Dragon Mantle Drannith Stinger Electric Revelation Ember Shot Enthusiastic Study Epiphany Storm Exocrine Expedite Explosion of Riches

This would be amazing and rewarding in any other situation, but it meant seeing our life points going down ridiculously fast while most of us had to discard tons of cards at the end of each turn because of the hand limit
And with black mana around, the player will probably have access to reanimator effects like Bladewing the Risen to get back some of those fallen Dragons