Don't hit into seed shroud. Yes, very hard I know, learn to control yourself.
Don't fight them in petals(you can't use guard skills and summoner heals inside, plus negates any evasion if you have that kind of buff)
Don't fight them on grass nettles(you get constant damage and you can't use defensive skills like SS). Also you need make much BNS gold to improve your equipment.
They have iframes on:
.E(Ali Cat return) every 30s from cast + knockdown or knockback
.iframe on X(for 5s or sometimes heal)
.4F(seed shroud + F makes them immune for 1 second after seed shroud)
Do not use aerials(unless you have 100% eva buff and not standing inside petal). This gives summoner time to send cat to you and knock you out of your combo.
Summoner Tab(2) is when they SS but turn invisible. This is key, but remember they can still get out of combo using:
.E cat recall(this can be used when stunned, daze, knockdown),
.V cat trip or bomb(bomb is dangerous, can ignore block, parry, etc.),
.C cat hammer daze
.Tab cat stun
You can try to kill the cat, but remember don't hit into it when they taunt, else you will heal the cat.
Summoner can use 4F to protect the cat too(makes it go invisible if you hit it with dandelion up)
Summoner can also SS to give 50% damage reduction and a 10% heal if they spec into it.
That is most if not all defensive abilities summoners have, now go practice and don't complain when you make mistakes if you ignore what I said above.
All above are only for refference. For more information, please go to http://www.bladesoulgold.net