Target creature gets +X/+0 until end of turn.

Whenever a creature attacks, flip a coin. If you win the flip, the next time that creature would deal combat damage this turn, it deals double that damage instead. If you lose the flip, the next time that creature would deal combat damage this turn, prevent that damage.

Target creature gets -1/-1 until end of turn for each artifact you control.

Cumulative upkeep or (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
When Jötun Owl Keeper dies, create a 1/1 white Bird creature token with flying for each age counter on it.

Enchant creature
Enchanted creature has first strike.
Threshold — Enchanted creature gets +3/+0 as long as seven or more cards are in your graveyard.

Whenever you cast a Spirit or Arcane spell, target creature can't block this turn.

: Prevent the next 1 damage that would be dealt to each creature and each player this turn.

Cumulative upkeep (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
: Kjeldoran Javelineer deals damage equal to the number of age counters on it to target attacking or blocking creature.

, Discard a card with converted mana cost X: Knollspine Invocation deals X damage to any target.

If an opponent controls a Plains and you control a Mountain, you may cast this spell without paying its mana cost.
Haste

Whenever Laccolith Whelp becomes blocked, you may have it deal damage equal to its power to target creature. If you do, Laccolith Whelp assigns no combat damage this turn.

Whenever a creature you control deals combat damage to a player, that player discards a card.

Attach target Equipment to target creature. (Control of the Equipment doesn't change.)

When Minotaur Explorer enters the battlefield, sacrifice it unless you discard a card at random.

All combat damage that would be dealt to you this turn by target unblocked creature is dealt to its controller instead.

You may sacrifice two Mountains rather than pay this spell's mana cost.
Create two 1/1 red Goblin creature tokens.

: All creatures able to block Mortipede this turn do so.

, : Shuffle your library.

At the beginning of your upkeep, put a +1/+1 counter on Myr Prototype.
Myr Prototype can't attack or block unless you pay for each +1/+1 counter on it.

Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
Whenever Nagao, Bound by Honor attacks, Samurai creatures you control get +1/+1 until end of turn.