Pay 1 life: Carrion Howler gets +2/-1 until end of turn.

Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, counter that spell if it has the same converted mana cost as the revealed card.

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
Sacrifice a creature: Regenerate Dimir House Guard.
Transmute (, Discard this card: Search your library for a card with the same converted mana cost as this card, reveal it, and put it into your hand. Then shuffle your library. Transmute only as a sorcery.)

: Mantis Engine gains flying until end of turn. (It can't be blocked except by creatures with flying or reach.)
: Mantis Engine gains first strike until end of turn. (It deals combat damage before creatures without first strike.)

Trample
Whenever Phyrexian Negator is dealt damage, sacrifice that many permanents.

: Add .
: Phyrexian Totem becomes a 5/5 black Horror artifact creature with trample until end of turn.
Whenever Phyrexian Totem is dealt damage, if it's a creature, sacrifice that many permanents.

(: Add .)

Creatures you control get +0/+5 until end of turn.

, , Exile Thran Foundry: Target player shuffles their graveyard into their library.

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
Counter target activated or triggered ability. If a permanent's ability is countered this way, activated abilities of that permanent can't be activated this turn. (Mana abilities can't be targeted.)