So you want to play Dekker?
Dekker is, in my opinion, an offense support; she has CC galore and so-so mobility, but a stun and a slow usually aren’t enough to save your carry’s hide in a surprise gank, so YOU need to be aggressive with your carry and dominate your lane.
How do I be aggressive so much?
Because Dekker has a ranged stun, you can use it to engage and win several damage trades during the laning phase. Try to take out their ranged minion first before going in, so you’ll take less damage (those guys really hurt more than you’d think).
Use only your basics to soften them up and stir up some panic, and then when they make a predictable move/escape, stun and go in for the kill. Set up the slow bubble right behind them and they’re either dead or have to back, which is a win either way, as they will slowly fall behind.
Once you have your Ultimate, let the enemy push up further, giving your jungler room to gank. Before they know he’s there, use your cage to trap them and they become fish in a barrel for the three of you. Stun them as the cage goes down and they aren’t going anywhere for at least 5 whole seconds, which should be more than enough time to get two assists for you and two kills for your carry.
ALWAYS REMEMBER TO GET WARDS AND GET RID OF ENEMY WARDS WHEREVER POSSIBLE.
Dekker is an offense-based Support, and should be played as such if you want to win. Later into the match, always remember to stick to your carry or team, and always be looking for good opportunities to ult.