When another green creature enters the battlefield under your control, both Ivy Lane Denizen’s triggered ability and Scurry Oak’s Evolve triggered ability will trigger (see and ). These triggers go on the stack and you (the controller of those triggers) order them; the order you choose affects whether Scurry Oak gets counters from Evolve because Evolve checks the comparison again when it resolves (Ruling [2021-06-18]). Ivy Lane Denizen can target Scurry Oak with its ability (Ruling [2020-11-10]).
Step 1
A green creature enters the battlefield (its controller put it onto the battlefield when its spell resolved) per ; that event causes Ivy Lane Denizen’s triggered ability and Scurry Oak’s Evolve triggered ability to trigger per .
Step 2
Put both triggered abilities on the stack. If you control both triggers, you choose their relative order as you put them on the stack.
Step 3
If Ivy Lane’s ability resolves and it targets Scurry Oak (allowed by Ruling [2020-11-10]), it puts a +1/+1 counter on Scurry Oak; that is an event of one or more +1/+1 counters being put on Scurry Oak and will trigger Scurry Oak’s Squirrel-creation ability.
Step 4
When Scurry Oak’s Evolve trigger later resolves it rechecks the entering creature versus Scurry Oak’s current power/toughness at that moment; if the entering creature is not greater in power or toughness, Evolve does nothing (Ruling [2021-06-18]).
Step 5
If instead Evolve resolves first and places a +1/+1 counter on Scurry Oak, that will trigger Scurry Oak’s Squirrel-creation ability; when Ivy Lane’s ability later resolves it may put an additional counter and trigger Squirrel-creation again.
Resolution
If a green creature enters and you control Ivy Lane Denizen and Scurry Oak, both triggered abilities trigger (Ivy Lane’s “Whenever another green creature you control enters…” and Scurry Oak’s Evolve) per and . You put both triggers on the stack and order them (AP/NAP ordering rules). If Ivy Lane’s ability resolves first and it targets Scurry Oak (which it may do per Ruling [2020-11-10]), it will put a +1/+1 counter on Scurry Oak; that will cause Scurry Oak’s “Whenever one or more +1/+1 counters are put on this creature…” ability to trigger and may create a 1/1 Squirrel token when that trigger resolves. Because Evolve rechecks the entering creature vs. Scurry Oak when it resolves, putting a counter on Scurry Oak before Evolve resolves can make Evolve no longer find the entering creature greater and thus Evolve might do nothing (Ruling [2021-06-18]). If Evolve resolves first and puts a +1/+1 counter on Scurry Oak, that also triggers the Squirrel-creation ability; when Ivy Lane later resolves it can add another counter (and trigger Squirrel-creation again). Continuous effects that change power/toughness between triggering and resolution are taken into account when comparisons are made per .
