Caldera Yeti
1R
Creature - Yeti
1/1
T, Reveal a red card from your hand: Caldera Yeti deals 1 damage to target creature or player.
Living in the heart of the mountains, these Yeti find both seclusion and power.
Rampaging Glyptodont
4R
Creature - Beast
3/3
Reveal a sorcery card from your hand: Rampaging Sasquatch gains haste and first strike until end of turn.
Glyptodonts normally rely on their thick, armored hide for protection, but when provoked, they will lash out with their spiked, club-like tails, destroying any predators foolish enough to attack them.
Thought Elemental
4U
Creature - Elemental
3/3
Reveal an instant card from your hand: Thought Elemental is unblockable this turn.
Foolish apprentices will often summon thought elementals to impress their peers, not realizing that the creature's ponderous movements reflect not its own nature, but theirs.
Spirit of the Eastern Sky
3WW
Creature - Spirit
3/3
Reveal a card from your hand: Spirit of the Eastern Sky gains protection from that card's types until end of turn. (The card types are Artifact, Creature, Enchantment, Instant, Land and Sorcery.)
Dawn breaks. She does not.
Corpse Digger
2BB
Creature - Zombie
3/3
Reveal a Zombie card from your hand: regenerate Corpse Digger.
Their natural feeding habits make them ideal for uncovering future minions. —Nevinyrral, Necromancer’s Handbook
- Caldera Yeti, Rampaging Glyphodont and Thought Elemental are perfectly fine. They're stronger than the Champions block variations on Red pinger and 5 mana 3/3s, but not problematically so.
- Spirit of the Eastern Sky is an absolutely amazing limited card. 3/3 flyers for 5 mana are generally high picks, even when they have a largely irrelevant ability (Aven Windreader, Aven Soulgazer, Mistform Shrieker). The Spirit's ability is a top-quality one though, and so I think it needs to go up to 6 mana and be uncommon.
- Corpse Giant is a Hill Giant with a good ability. Vanilla Hill Giants are surprisingly powerful in limited (see: Order of the Sacred Bell from ChK) and free regeneration is also very good. Again, I would add a point of mana and make it uncommon, especially given that black is not supposed to get better midsize creatures than green.