Limited: Modern Masters combat tricks

Beware of 1W.

Common instants to expect in combat:

1W Otherworldly Journey
1W Test of Faith
4W Gleam of Resistance

1U Spellstutter Sprite
1U Echoing Truth
2U Erratic Mutation
2U Pestermite

B Peppersmoke
2B Drag Down
1BB Horobi's Whisper

R Brute Force
1R Glacial Ray
1R Crush Underfoot
1R Fury Charm
3R Torrent of Stone
5R Fiery Fall

1G Echoing Courage

The cards in italics mostly won't be in people's decks. There are "Giant Growths" in all three Naya colours (Test of Faith, Echoing Courage, Brute Force). There is also a bunch of red and black instant removal.

Horobi's Whisper and Torrent of Stone both have non-mana splice costs, so an opponent with U untapped can still just cast Reach Through Mists and splice to kill a creature.

Commons to not get killed by:
2W Blinding Beam

5WW Ivory Giant

2B Deepcavern Imp
6B Absorb Vis

3RR Thundering Giant

These ones aren't pump spells or removal, but they can still surprise-kill you. Two of them are white commons that will tap all your guys.

Common counterspells to not walk into:
1U Spellstutter Sprite
UU Logic Knot
3UU Traumatic Visions

I don't know if many people really play these counterspells, but two of them have another mode, at least (Spellstutter Sprite as a 1/1 flyer and Traumatic Visions to dig for land).

Rebels that your opponent might search for:
(in order of how much to fear them)
Bound in Silence
Rathi Trapper and Saltfield Recluse
Amrou Seekers and Avian Changeling
Blightspeaker
Deepcavern Imp
Amrou Scout
Mothdust Changeling

3 of the searchable commons can shut down an attacker, and another 3 of them have 2-power and evasion.

A specific common that forces you to always block Mothdust Changeling:
(2U) Latchkey Faerie

Watch out for Latchkey Faerie!