Whether this means tapping their creatures, limiting when they can play spells/abilities, mana tax, or sacrificing permanents, all of these count as using a STAX strategy
8 Dome Fossil The Ancient Vampire Summoner The Dome Fossil is required to play Kabuto, and its evolution, Kabutops
Let's say you're playing Collected Company

Synthoids Aang and Katara Aang and La, Ocean's Fury Aang, A Lot to Learn Aang, Air Nomad Aang, Airbending Master Aang, Destined Savior Aang, Master of Elements Aang, Swift Savior Aang, at the Crossroads Aang, the Last Airbender Aarakocra Sneak Aardvark Sloth Aatchik, Emerald Radian Abaddon the Despoiler Abattoir Ghoul Abbey Gargoyles Abbey Griffin Abbey Matron Abbot of Keral Keep Abdel Adrian, Gorion's Ward Aberrant Aberrant Manawurm Aberrant Mind Sorcerer Aberrant Researcher Abhorrent Oculus Abhorrent Overlord Abigale, Eloquent First-Year Abigale, Poet Laureate Aboleth Spawn Abolisher of Bloodlines Abominable Treefolk Abomination Abomination of Gudul Abomination of Llanowar Abomination, Irradiated Brute Abomination, Terrifying Titan Abomination, World Ravager Aboroth Aboshan, Cephalid Emperor Absolute Virtue Absolver Thrull Absolving Lammasu Absorbing Man Absorbing Man and Titania Abstract Iguanart Abstract Paintmage Abstruse Archaic Abu Ja'far Abuelo, Ancestral Echo Abuna Acolyte Abundant Maw Abyssal Gatekeeper Abyssal Gorestalker Abyssal Harvester Abyssal Horror Abyssal Hunter Abyssal Nightstalker Abyssal Nocturnus Abyssal Persecutor Abyssal Specter Abzan Battle Priest Abzan Beastmaster Abzan Devotee Abzan Falconer Abzan Guide Abzan Kin-Guard Abzan Skycaptain

They are popular for vintage openings or for collectors who want to own a piece of TCG history.