Hi, if I attack with a 6/6 Kalonian Hydra and my opponent blocks with a 3/3 elemental token with Omnath, Locus of Rage on the field, do I still do 3 trample damage to my opponent or does Omnath's ability kill my hydra before any trample damage goes through?
Combat damage is all deal simultaneously unless First Strike or Double Strike is involved. That means that for your scenario, Kalonian Hydra deals 3 damage to the token and 3 to the defending player at the same time. The 3 damage is marked on the token and the next time State Based Actions are checked (immediately prior to a player getting priority) it will die. This will cause Omnath to trigger and Omnath's controller can then deal 3 damage to your Hydra if they want to kill it, but that won't retroactively remove the damage it has already dealt.
Damage