Kresh the Bloodbraided

Whenever another creature dies, you may put X +1/+1 counters on Kresh the Bloodbraided, where X is that creature's power.

Mage Slayer

Whenever equipped creature attacks, it deals damage equal to its power to the player or planeswalker it's attacking.
Equip {3}

If one or more +1/+1 counters would be put on a creature you control, twice that many +1/+1 counters are put on it instead.

Castle Embereth enters tapped unless you control a Mountain.
{T}: Add {R}.
{1}{R}{R}, {T}: Creatures you control get +1/+0 until end of turn.