Against Burn, I have a single COP:Red in my Enlightened Tutor board. It comes down turn three most games, and as long as they don't have a god hand, that's fast enough to stop them. Mono-red can only effectively answer COP with Chaos Warp, if they have it; Pridemage deals with the rest of their SB. It's important to get your life gain online ASAP after sticking the enchantment though, or the Burn player will just wait 'til they have more spells than you do mana.
Against combo:
I feel like out best options are Teeg, Canonist, and Thalia/Thorn of Amethyst. The creatures are better because they can be protected my Mom, which is a big deal. The only reason I'm not sold on Thalia yet is that unlike the other two we (I) have no way to search for her, and being legendary means I don't want to maindeck more than one. Thorns get really good in multiples, and Thalia doesn't.
In my SB, I also have a single Ratchet Bomb (wish it were E. Explosives) to deal with token strategies, including Belcher, a Stony Silence for their artifact mana, and a Pithing Needle for everything from Goblin Charbelcher to Candelabra of Tawnos.
I learned the hard way that some combo decks, especially Belcher, will just shrug at an Ethersworn Canonist, play a bunch of 0cc artifacts, and combo off anyway.