I have Rengar legend. I have a 4 might unit in base. I play Kinkou Initiate in base giving +1 to my 4 might unit pushing her to 5 might. Do I draw a card?

Yes, you can draw a card in this scenario.

The Ruling

When you play Kinkou Initiate, both its "When you play me" triggered ability and your Pridestalker (Rengar Legend) triggered ability trigger simultaneously because they share the same trigger condition ("When you play a unit").

As the controller of both abilities, you choose the order in which they are placed onto the chain (Rule 333.1). To ensure you draw a card, you should sequence them as follows:

1. Play Kinkou Initiate: It enters the battlefield.
2. Place Triggers on the Chain: You choose the order. Place the Kinkou Initiate ability on the chain first, then place the Pridestalker ability on top of it.
3. Resolution (LIFO - Last-In, First-Out):
   • The Pridestalker ability resolves first: You target your 4-might unit and give it +1 Might. Its total Might is now 5.
   • The Kinkou Initiate ability resolves second: It checks the total Might of your other units. Since your unit now has 5 Might, the condition is met, and you draw a card.

Important Notes

• Total Might: Kinkou Initiate's ability checks the total Might of all your other units on the board at the time of resolution, not when the unit is played.
• Timing: Because the Might check occurs on resolution, you can use effects like Pridestalker to buff your units into the required range before the Kinkou Initiate ability checks the board state.

This interpretation is based on the standard LIFO resolution of the chain and the rules regarding simultaneous triggers. This is supported by RiftJudge FAQ #9873 and #10585.