Yet another card dump (Circeus's): Mechanics

Mechanics

*Constellation* —: Used on 1 cards: Earthbind

Scrycling: PARAM1, Discard this card: Scry 1. Used on 1 cards: Weeping Forest

Pretty sure this has been independently designed many times.

Latch: If the last spell you cast this turn had a converted mana cost of PARAM1 or higher, you may cast this spell for its latch cost. Used on 6 cards: Arcane Deductions, Encroaching Nature, Poison Cloud, Sudden Growth, Spell Sluice, Sanity Leech

*Ferocious* --: Used on 3 cards: Downslope Assault, Cliffside Collapse, Freezemist Shaman

Ethereal: You may cast this spell for its ethereal cost. If you do, it enters the battlefield as an enchantment with no other types or subtypes. Used on 10 cards: Adikia, Reflection of Injustice, Oizys, Daughter of Woe, Eryma, Defender of the Meek, Geargrit, Juniper Spirit, Poine, Hand of Retribution, Sophrosyne, Who Moderates, Shadow of the Griffin, Ardorweave, Homonoia, Soul of Concord

Dismiss: Whenever this spell becomes the target of a spell or ability, you may pay PARAM1 to return it to your hand. Used on 3 cards: Double the Guards, Flustered Sprite, Dismissive Lightning

Operate: PARAM1: Attach an unattached creature you control to this artifact. An attached creature can't attack or block. Operate only as a sorcery. Used on 3 cards: Pendulum Engine, Microbe Suit, Jäger Suit

Obviously, Operate has ruling exceptions comparable to Bestow.

Surge: You may cast this spell for its Surge cost. If you do, change its text by increasing all numbers by one. Used on 1 cards: Entropic Siphon

Gossamer: Whenever this creature blocks or becomes blocked, you may return it to your hand. Used on 4 cards: Ethereal Killer, Wisps of Will, Poison Elemental, Wild Bladeswinger

Escalate: Then any opponent may pay this spell's escalate cost and copy it. They may choose new targets for the copy. Used on 10 cards: Plagiarize, Flay the Enemy, Sudden Recall, Abject Refusal, Metempsychosis, Spider's Leap, Cleansing Pulse, Parasitic Explosion, Expunge, Expose the Corrupt

Iridescent: This creature gets +1/+1 for each color amongst permanents you control. Used on 2 cards: Chromatic Bear, Chromatic Sprite

Second Wind: Exile this spell at it resolves. At the beginning of the next end step, if it was exiled that way and you cast no other spell this turn, put it into your hand. Used on 1 cards: Troll Brothers

*Raid* —: Used on 1 cards: Blood Festival

Deranged: You may discard a card in addition to any other costs as you cast this spell. If you do, it enters the battlefield with haste and indestructible until end of turn. Used on 2 cards: Fireweaving Chimera, Revelbones

Sublimate: You may cast this card face down as a 2/2 creature for {3}

. Cast it as a noncreature spell while face-down for its sublimate cost. Used on 2 cards: Elemental Annihilation, Vortex of Claws

scry: Used on 3 cards: Doompeek, Meletian Swordbound, Machaimancer

Outshine: Whenever you cast a noncreature spell, you may pay PARAM1. If you do, put a +1/+1 counter on this creature. Used on 1 cards: Street Performer

*Xenophobia* --: Used on 3 cards: Revisionist Mage, True Berserker, Xenophobe Boy

Whenever ~ becomes blocked by a nonX creature,

*Inspired* —: Used on 1 cards: Machaimancer

*Strive* —: Used on 1 cards: Ultimate Assault

*Heroic* —: Used on 1 cards: Feller of Hydras

Garrison: You may have this creature enter the battlefield tapped. If you do, create a 1/1 white and red soldier creature token. Used on 1 cards: Boros Quartermaster

Bulwark: Whenever you cast a creature, you may pay an additional PARAM1. If you do, that creature enters the battlefield with an additional +1/+1 counter on it. Used on 1 cards: Shellmaker Tortoise

Prowess: Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn. Used on 4 cards: Monastery Overseer, Sacred Chamber Wayholder, Monastery Archeologist, Bloodfire Apprentice

Bolster: Choose a creature with the least toughness among creatures you control and put PARAM1 +1/+1 counter on it Used on 4 cards: Spiritual Defenses, Bolstering Growth, Slice Bones, Aven Cloudburster

Manifest: Put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card. Used on 1 cards: Soul Snatch

Delve: Each card you exile from your graveyard while casting this spell pays for {1}

. Used on 3 cards: Soul Impression, Spiritual Defenses, Erupting Sibsigs

Soulbond: You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them. Used on 1 cards: Dryad of Plenty

Outlast: PARAM1, {t}

: Put a +1/+1 counter on this creature. Outlast only as a sorcery. Used on 2 cards: Wastes Survivalist, Parapet Sentinels

Mana trail: Whenever you cast another spell with mana trail, if this is in your graveyard, you may cast it from your graveyard. If you do, exile it as it resolves. Used on 1 cards: Trail of Strength

An idea.

Landlock: This aura comes into play attached also to a land with the same controller as its normal target. Used on 5 cards: Pestiferous Emanations, Fire Regurgitation, Freezer Burns, Rainbow Sprout, Strikes from Below

Bide time: If you cast this spell during your main phase, you may draw a card, then discard a card. Used on 3 cards: Duskmantle Circler, Just an Accident, Sudden Impediments

A Dimir idea from here

spy: To spy, choose land or nonland, then reveal the top card of that player's library. Used on 6 cards: Recoverer of Secrets, Hijack Vigor, Dimir Mindstabber, Pervade Thoughts, Heft of Thoughts, Dimir Spy

A reworked Seek Fate for Dimir. Idea from here

Engage: As an opponent's combat phase begins, you may have this creature block this turn if able. Used on 1 cards: Prepared Warrior

In card text or details pages, write the mechanic's code name (playtest name) between square brackets, like "[Crittercast]", "[Bushido 1]" or "[Delay 4 {2}{R}{R}]". It will be expanded to the mechanic's name plus reminder text, such as "Suspend 4 – {2} {r} {r} . (Rather than cast this spell from your hand,...)"
To expand a mechanic's name but not its reminder text, include parentheses at the end of the square brackets: "[Crittercast()]", "[Delay 9 {R}()]".