The mechanic itself is discussed here:
http://www.themanadrain.com/index.php?topic=29421.msg431193#msg431193
Guardian of Valor

Creature-Human Guardian (C)
2/3
Accumulate- At the beginning of your upkeep, put a hoard counter on this permanent.
Remove two hoard counters from Guardian of Valor: Untapped creatures get +0/+2 until end of turn.
Guardian of the Moon

Creature- Human Guardian (C)
2/2
Accumulate- At the beginning of your upkeep, put a hoard counter on this permanent.
Remove two hoard counters from Guardian of the Moon: Draw a card, then choose and discard a card.
Guardian of Twilight

Creature- Human Guardian (C)
3/3
Accumulate- At the beginning of your upkeep, put a hoard counter on this permanent.
Remove two hoard counters from Guardian of Twilight: Target player discards a card. Use this ability only whenever you could play a sorcery.
Guardian of the Flame

Creature- Human Guardian (C)
3/3
Accumulate- At the beginning of your upkeep, put a charge counter on this permanent.
Remove two hoard counters from Guardian of the Flame: Guardian of the Flame deals 2 damage to target player.
Guardian of Nature

Creature- Human Guardian (C)
2/2
Accumulate- At the beginning of your upkeep, put a charge counter on this permanent.
Remove two hoard counters from Guardian of Nature: Target creature gets +1/+1 and Trample until end of turn.
These are made mainly for limited, so they are not allowed to be too good. They sgould also represent segments of the colour pie. Currently, I'm not completely satisfied with some of the names and the creature Types (should be more individual), and the "stats" and abilities are open for discussion, too. So, feel free to suggest improvemenents for these five cards (remember that they will be commons, so no complex or very good ability). Should all be on a similiar power level, I think, so if one is better than the others, I would appreciate your tweaking.