I like the GF and junction system from FF8 drawing magic and investing magic to improve your stats and the GF thing is pretty fun in fact I think the whole system became a thing cuz square looked at the sort of crazy animations they made for GFs and went "man it would be a waste if shiva and ifrit become useless in the late game why not come up with a system that prolongs all summons usefulness" also the gunblade being able to deal more damage when you press R1 was very cool I figured this Interaction with the gunblade at disc 4

realized what made gunblade so cool and why everybody wanted one.
Also the materia system from ff7 allowed for more specialized spellcaster builds you can't just cast all spells so you end up with a small and powerful collection with spells it does help that you are playing as cloud a jack of all trades protagonist a decent spellcaster not the best but works.
WarCraft 3 hero system is pretty engaging along with the mercenaries mechanic and shops around the map make for a very intractable world.
Red alert 2 super weapons I think they can be considered a mechanic of their own but we have whats a mechanic in the first place?
Age of mythology mechanic of advanced to the next age through offering 2 choices to choose from that suit your playstyle unless you play RTS without a plan then idk what to tell you but to at least figure what units you want to make in the game.
And the toggling of first person and third person in metal gear solid and the radio mechanic I forgot the exact device name but its basically an advanced radio that allows you to speak with different characters throughout the game not using this mechanic means you will get a worse experience playing metal gear solid.
The radio mechanic from silent hill 1 a way to spot monsters but adds to the fear and tension double edged sword lol.
Also shooting in silent hill 1 unlike resident evil where your shots never miss you play as your average dude in silent hill not exactly a police officer so your aim kinda sucks shooting a target far away results in missing the shot , shooting multiple times in rapid succession also makes you miss.
These are enough to satisfy the reader I think.